UPDATED 21 August 2015:
[Links, pretty pictures, and more!]
colorfilter - Their big 40 pack of icon textures (download link at Facebook here) is still the one I use most often and I haven't begun to scratch the surface of the hundreds of textures within. Also check out the pack of larger 800x600 textures. You can also find the sets posted individually on their journal. I've posted a few more examples of my icons using these textures in the comment thread here.
texturize - (Many thanks toteragramm for rec'ing this community) One-stop shopping for anyone interested in creating and sharing textures. Be sure to read the comm's very informative "Bible" (guidelines) before posting or snagging. Most of the artists post links back to their graphics journals or to Deviant Art. Some of my favorite member-artists:
lookslikerain at soaked. I've used more of their textures than anyone's except colorfilter's:
jordannamorgan at wolfbane_icons
scoobyatemysnax at burnedbreads - includes tutorials.
FRAMEs & BORDERs for use - Flickr image sharing group
Victorian Frame Company
SCREENCAP RESOURCES for Buffyverse
slayerstillness has a list of Screencap Resources for BtVS and AtS, including all the ones I use most frequently; if you know of any not on the list, send the links to starry_night. Some of my favorites from the list:
* Pretty as a Picture complete screencaps for BtVS and AtS plus promo photos for Buffy
* Bloodqueen also has all seven seasons of BtVS complete
* Leave Me the White - Spuffy-centric so no S1 or S3 caps and the remaining seasons are incomplete; but the best quality caps of the series
I've found. (S2 is the most complete with 14 episodes capped.) Includes Dailies for Smashed and Dead Things. S7 is spread out over
three albums including two Miscellaneous albums. Also Veronica Mars caps for all three seasons.
OTHER IMAGE SOURCES
* The British Library offers over one million royalty-free digitized images from their vast archives going back to the 17th century.