I've recently started using more and more of these, jpg images of characters or monsters or other things, as a play aid.  I figured since my computer is right there, and sometimes it can be very helpful in campaigns the size I make them, where there are literally dozens and dozens of NPCs the PCs have to know about at once, it certainly makes it easier for my players if they can see pictures, instead of having to rely on my descriptions for every single one of the characters.

So does anyone know of any sites that have good images, pictures of characters, or of monsters, or of places, fantastical or futuristic?

In my case, I've been collecting Jpgs of the Legion of Superheroes characters from all over the net, pictures of Roman Emperor's statues again from googling, and images of characters from the Three Kingdoms mostly from this wiki site which has all the images from DW.

RPGPundit

Epilogue.  Who's your buddy, Pundit?  Who's your pal?

yeah,www.conceptart.org


now, who's your buddy?

http://www.conceptart.org/

´Nuff said.

EDIT: Fuck! You bet me to it!
Me wanna be Pundit-buddy!

All that's left for me to do is to say: At conceptart, make sure to check out the Best Of forum. And sit down before you do.

Videogame developers are always a great source for concept artwork.

On that note, Lineage II. I use images from that all the time (airships, cities, Elves, palaces...).

How about WotC's art galleries? They have the artwork for most of their books available for download, and much of it is pretty damned good:

http://www.wizards.com/default.asp?x=dnd/arch/ag

Ditto for Epilogue.  I'll browse the pages of new stuff until I spot an artist that I like and look at their stuff more deeply.

How about Munchkin Press?

I just found it via The Art Department blog.

Which I found a long time ago via the Whatever blog by John Scalzi. (note I have not been to whatever in a long time... nor The Art Department).

I suppose I should pimp my studio.  . . so you can find some high quality artwork at //www.emptyroomstudios.com

we also have an art section at //www.tangledmuse.com

www.deviantart.com is the last of what I consider the big three for me (the other two have already been mentioned).

Some of the things I often use for images for personal (not for publication or profit) use in gaming is the various stock photography agencies.  Lots of stuff for various locations, terrain, etc.