would google maps with their pins work?

I mean to say, I know it would work, but would it generate the type of image you need

You can do some map graphs in Excel:
http://www.techrepublic.com/article/put-your-excel-data-on-the-map/5029707
http://www.gislounge.com/creating-simple-maps-with-ms-excel/
http://www.gislounge.com/making-maps-within-excel/
http://www.andypope.info/ngs/ng12.htm

Firas, it might work, but how do I get the 5,000 pins on the map without going insane? can I upload a file somehow?

Thanks theora55 - I'll have a look at those.

dg what format are the locations in? Ultimately we'll need long/lat coordinates to give to the Google Maps API but we might be able to generate them using some API from whatever address format you have somehow

The locations are addresses, with street address, suburb, state, postcode (I can generate them in various formats, but our default reporting output is Excel). I'm just looking at Google Maps Engine Light, but it only allows up to 100 points. Google Maps Engine allows more points, but needs things like shape files that I can't do. I'm also looking at Target Map (found from one of theora55's links), but I'm not sure if it gives me what I want - will have to try it at home and see what it spits out. I'm a little uncomfortable that it requires maps to be shared, though.

Have you looked at BatchGeo? It's super simple, and has worked for me.

GeoCommons is what you want. You can upload datasets in .csv and then visualize them on any one of a number of base maps (and do things like change size, color, etc). If you were able to download software and had some knowledge of CSS, I'd recommend MapBox + TileMill.

Oh, I missed the part about the locations being addresses. I believe GeoCommons has a feature that will find the lat/long coordinates based on address, but I could be wrong.