This thread with blank maps of nearly every part of the world should be useful.
After doing a little research and what not, I realized all those big software map making programs are a little too much for me. What I'd like to find is a library of pre-made "base" world maps.
Are there any large world maps that are for use by anyone? I'm using MapTool, so I will add my own stuff to it. Just looking for a map I can download and from there, add all my trimmings to it.
Are you talking real world or fantasy? If real world, the link Sapiento provided is probably the best; that's got so much stuff in it by now that it'll probably take you days just to look through it all.
If you had fantasy maps in mind, you can actually create your own base maps fairly easily if you have photoshop or an equivalent. Just use the Clouds filter, then adjust the contrast down to a sharp black and white, and you should have a nice spread of 'continents' and 'islands' which you can then mash up and move around at your leisure.
Check out the finished map sections with the thumbnails thread and if you like some of them, check the usage policy or contact the poster.
We have a CWBP - Community World Building Project where we have mapped a large area and have wiki descriptions for most of the places. Thats CC licensed with NC-BY-SA so pretty liberal and no problem for VTT style playing.
If budget is an issue, GIMP is great and there are a bunch of bonafide GIMP-Nerds around the place who can lend a hand.
If you have use for any of the ones I've made, let me know, I'd be happy to set up unlabelled versions (or even make available PSD versions with the lavels attached and ready to rename, or whatever).
My finished maps
"...sometimes the most efficient way to make something look drawn by hand is to simply draw it by hand..."