Some of us don't have sites sicne we work at this very part time. I do instead a periodic list to to art colelctors who send me their emails- it's usually 13-16 pages long - major focus is comic book and comic strip art but it includes illustration art and a small amount of obscure animation including silent film era. I get newer post 1970 art but a lot of the list is older material- Iger shop, Classics illustrated, harvey, Dell and standard- the superhero art often moves fast.
If you want a list email me at email@example.com I also work off of want lists a lot and between lists just contact people if art turns up they are looking for. Best George Hagenauer (yes the person who does the Comic Buyers Guide pieces on Art) I will be off line a lot the first two weeks of October 2007 due to a number of other committments so if responses are delayed that is why