I've seen this done on home shows - 'invisible' shelves' or floating shelves.

There's a ton of stuff on Google showing how to do this and it looks great when it's done.

If you have the bookcase style shelves that are a piece of furniture, you shim the bottom at the floor to level. Likewise, shim the back to vertical plumb.

If you want the look of simple shelves such as essexjan suggests, then these can be at any/ variable heights. be sure to attach to something secure in the wall - 2x4 or such. For the bottom, rather than locating a shelf at floor level, consider using this space for containers such as baskets, decorative boxes or such.

Why not just clip off the bottom corner of the shelving unit to accomodate the baseboard?

I'd do something with doors at the very bottom.
The shelves I have that go all the way to the (hardwood) floor tend to get nasty- cat hair collects on the books and stuff.

If it were me, I'd stop the bottom shelf 3' above the floor so you don't lose the floorspace under the shelf for a chair or plant or something. Also easier to vacuum under.

re: ShelfBar's "How strong are our shelves?"

Notice where his weight is focused, at the back of the shelf on the bracket and not really on the shelf itself.

I would build a complete unit with a plywood backing, as you suggest and fix it to the wall (with lots of screws if you plan to fill it with books). If you can afford to lose the shelf space, leave enough room underneath to put other things. If you need/want to go all the way to the floor with the shelving, you need to put a kick panel under the bottom shelf and you can also adjust this to level things out. If the shelf unit is to be permanent, you can leave the kick unit separate and plane it to suit the floor so that you start with a perfectly level base (or at right angles to the wall if that is more important). You can also make the end panels slightly deeper than the rest of the unit and plane them to fit the walls to give that "built-in" look. It all depends on either your budget or your ability/time.

Thanks for the tips, all. Those floating shelves are way cool, but I think I'll go the cheap route:

I would build a complete unit with a plywood backing, as you suggest and fix it to the wall (with lots of screws if you plan to fill it with books). If you can afford to lose the shelf space, leave enough room underneath to put other things.

Exactly! And I'll be sure to use some heavy, tempered screws and hit studs all over when hanging.

:-)

Better than going crazy with visible screws is to use a French Cleat. A French Cleat makes hanging the cabinet a single person job.

In this picture the cleat is the narrow bar running between the two sides on the left hand side. The cabinet is 34" inches wide, 10" deep and 6' tall.
≡ Click to see image ≡
Because the screws used to mount the other half of the cleat are in shear they have lots of strength. Half a dozen 10 X 2 1/2" screws will easily hold hundreds of pounds if driven into a stud. This cabinet was only mounted with four screws yet it could support my mass.

Great idea, Mitheral. Of course, my shelf-set might be considerably wider than 3', but I could always do multiple shelves as above, making life much easier on myself when I hang them (probably by myself.) Thanks.