My basic dressing. . .

Olive Oil
Red Wine Vinegar (about a third as much as vinegar)
Half teaspoon of dijon mustard
Tarragon
A bit of grated parmesan
A clove of crushed garlic, or dehydrated garlic
A Dash of white pepper

I make my own salad dressing, but no mayo. I whisk together about a tablespoon of dijon mustard, a pinch of salt, and a tablespoon of white-wine or balsamic vinegar; once that's mixed together, I whisk in a couple tablespoons of olive oil. I pepper the salad, then pour the dressing over the peppered salad.

That's about enough for two biggish salads; scale up or down accordingly.

balsamic vinegar
olive oil
crushed garlic
salt
cayenne
oregano
basil
pepper

I make my own caesar salad dressing and it's quite tasty:

5-6 anchovy filets
5-6 cloves of garlic
1 egg yolk
juice from 1 lemon
~1/2 cup olive oil

Mix everything but the oil and, while mixing, slowly add the oil until you reach the desired taste/consistency. Add some salt as well, if required, I don't as I find the anchovies to be salty enough for me. This keeps overnight but I find the next day to be a little to fishy tasting for me so I usually just throw out whatever doesn't get eaten (which is usually not much as the boy and I like this quite a bit). I've also been toying with the idea of adding a teaspoon or so of whole grain mustard or dijon to see how that affects the taste. YMMV.

Most of the time we go minimal, with olive oil, lemon, garlic, salt, fresh ground pepper. It's nice to crush the garlic and put it in a small jar with olive oil and lemon, let it sit for some time before you are ready to eat, and then shake it up well and pour over the salad, straining the garlic.

Salt
Fresh Pepper
Olive oil
Balsamic vinegar
Whatever fresh herbs i have or whatever else i feel like using

Some people smash garlic into a paste and add with salt and lemon juice, or thin nayonaise with lemon juice and dijon mustard. It's all quite endless depending on what you have around.
i have an immersion blender now. i could make mayo. Hmm.

Maybe after i make butterscotch for the first time.

I used to work at a restaurant where we made a tarragon-mustard dressing. We made it in huge quantities. It was two large plops mayo, one large plop golden mustard, a cup of blended oil (I'd use olive if it were me,) a half cup of cider vinegar, a big handful of dried tarragon, salt, and pepper. Mix it with a whisk until it's dressinglike (lots of mixing). If it's still too thick, add more cider vinegar and oil in proportion until you like the consistency.

I hate mayo - I had trouble even looking at two big plops of mayo - and yet when finished, this dressing was actually pretty good.

Lots of umami ingredients (worcestershire sauce, oriental fish sauce, soy sauce, balsamic vinegar) pepper and an olive oil/mayo mixture. The mayo is for adhesive qualities to the greenery.

Vinaigrette salad dressing is like a 12-bar blues. It's a really simple basis for an infinite number of variations.

I like 50/50 oil/vinegar - some think that's too tart.

The basic vinaigrette is like 4T oil, 4T vinegar, 1/2t salt, 1/4t ground pepper.

From there you do simple variations but swapping oils and vinegars. I usually stick to olive oil, but you could use others (or a little bit of other oil - like truffle oil for flavor). I've used rendered duck fat as part of the oil. For vinegars, try cider, red wine, white wine, champagne, rice wine, sherry, etc (I don't include balsamic - see later). You can also use all lemon juice or part lemon juice.

Then there are flavorants:
dry or wet mustard (wet acts as an emulsifier - bonus!)
herbage (basil, thyme, dill, tarragon, oregano, rosemary, chives, parsley, cilantro)
fruit juice - lemon, lime, orange, pomegranate, mango, guava
Balsamic vinegar - doesn't have the same acid as regular vinegar and using the real stuff for a whole vinaigrette is pricey, but a splash in the mix is awesome

So here is one simple variation that will make an awesome dressing to go with a salad served with red meat:
4T olive oil
4T red wine vinegar
1t salt
1/2t pepper
1/2t finely minced fresh rosemary
1T Dijon mustard
Combine, shake well, dress.

Here's another
4T olive oil
3T rice wine vinegar
1T lime juice
1/4t grated lime zest
2T chopped cilantro
1t salt
1/4t pepper
Combine, shake well, dress

My most recent eek salad dressing consists of:

Olive oil
Vinegar (to taste, and whatever you like. I use what's handy. Good balsamic is nice for being mellow and sweet)
Dijon mustard
Soy Sauce
Sesame Oil
Honey
Coriander
Pepper

Mix in proportions that taste good to you. The Coriander adds a great lemony citrus flavor without tartness.

Lemon juice (from a lemon, not a plastic container) and olive oil (if you're not using extra-virgin/cold pressed then why bother?). Combine in a 1:2 ratio. Sesame oil (less than a teaspoon, about 3 dashes), balsamic vinegar (not lots), spices (I crush black peppercorns, mustard seeds, and either basil or roasted coriander seeds in a mortar until they're crudely ground), 1 diced clove of garlic (optional). Shake it all up and leave it for a bit. The longer it's left, the more the garlic will work. That's it. Takes about 2 minutes to make, what with pounding the spices.

Mayo. I have one of those little blender-things that go on the end of a Braun hand-held mixer. Makes enough for a few days, and always ensures it's fresh. From start to finish, the whole process is about 3 min and it's cheaper than buying the crap off the shelf.
1 egg, at room temperature.
1 tablespoon of vinegar / 1 tablespoon lemon juice.
1/2 tablespoon of mustard. The mustard's important, and I find a nice Polish or German whole grain, or crushed grain works really well.
Spices. I use various ones. Crushed black pepper corns, little teensy bit of sea salt, oregano/basil/tarragon/whatever else that's not too overpowering.
Olive oil. See the amount that's in the container with the egg and everything? Double that and add a little bit more.
Blend.
It's still runny, but it's supposed to be. Add either more olive oil in little bits, blend, add more oil, blend until it's firmed up, or switch to Canola or Safflower (they have less saturated fats) oil at this point to not make the mayo as rich.
Done.
(Note: we're walking a fine line here between having the mayo set and have it turn to soup. There's enough vinegar to react with the single egg and the oil. Any more moisture than what occurs in the ingredients naturally and it won't set. Basically, when you're adding the mustard, make sure that you haven't scooped up a lot of water with it, and don't overdo the vinegar.)

I should mention that my dressing recipe was adapted from elizard's original recipe, so all the credit goes to her.

Nice! I did a quick mix with mustard, mayo, olive oil and balsamic vinegar. The balsamic overpowers the mayo, but maybe something lighter next time. I had no idea how easy dressing is.

Naah. Just use less balsamic. Too much mustard can kill it as well - it's just a matter of finding a balance between all the flavours.

How did I miss this thread? Yep, my recipe's similar to Zack's. Actually it's almost exactly the same as taz's, except that I add a scant tsp of good mustard and about a tsp or so of mayo, which emulsifies the dressing. I've tried making it with various vinegars, but I really prefer the taste of fresh lemon. A few drops of sesame oil is really nice, especially with mixed greens.

You can also make a nice creamy dressing with mayo in it. I mix about a cup of plain yoghurt, 2-3 tbsp of mayo, some salt and pepper, about a tbsp of fresh lemon juice, and a whack of fresh herbs (chives are especially good, though I've also made it with curry powder instead of herbs, which also works really well).

I make my own mayo, too: Put 1 egg + 1 yolk (room temp) in a blender jar, add juice of 1 lemon, 1 tsp mustard, a scant tsp sea salt, pepper to taste. In a measuring cup, have ready 1/2 c extra-virgin olive oil and 1/2 c plain oil such as corn or vegetable. (I find that if you use more olive oil it overpowers everything and you don't get that nice, delicate mayo flavour.) Put the lid on the blender with the centre bit removed, blend the egg-lemon mixture for a few seconds, then slooooooooowly add the oil in a thin stream with the blender running. Et voila! Sometimes it's thicker than others, but it usually turns out pretty thick this way. If the mayo breaks (i.e becomes an unemulsified soup of blech--I've only had this happen once), pour it out into the measuring cup, put another egg yolk in the blender, and slowly add the broken mayo to the yolk with the blender running. This makes super-rich, neutronium mayo, which is not necessarily a bad thing.

Cleaning the blender after this is sooooo much easier if, after removing your yummy mayonnaise, you blend a cup of hot water, dump, repeat.