Along with some of the forum signatures I have made, I have posted a few links to the pictures I used in my signatures:

Links to easily find pictures to use:

http://planetrenders.net/
http://www.deviantart.com/?tier=stockart
http://www.istockphoto.com
http://www.freefoto.com
http://www.pictor.com
http://www.imagebank.com
http://www.ditto.com
http://www.bciusa.com
http://www.visipix.com
http://www.photo.net
http://www.webshots.com
http://www.gograph.com
http://www.freestockphotos.com
http://www.photonica.com
http://www.freeimages.co.uk
http://www.pro-visions.com
http://www.snap-shot.com
http://www.freemediaarchive.com
http://www.corbis.com
http://www.sibx.com
http://www.atpictures.com
http://www.cmyk-ink.com
http://www.eyewire.com/