Aside from AJ (who I probably should not be talking about due to a conflict of interest), I have had good luck with 618evan, lccoins, and kkccsmpb.
I've been dealing with vette1986 since the first time I used e-bay. He's pretty straight forward about what the thinks about the coin (doesn't give a tpg grade, but G/VG/F/XF/Etc). Everything I have got from him is as described and always shipped promptly & well packaged.
lmao indianhead... I buy from hocey too. Just like vette1986 they are both in my saved seller list. He has some neat deals from time to time in lots.
I have bought from valleycoin too, and the product was nice, just the shipping charge i wasn't too happy about. No biggie though, for as many deals I've gotten the one time shipping overcharge wasn't a biggy.
Here a few others I have bought alot of goodies from on e-bay and have as saved sellers: cknol1 - always has tons of morgans & peace dollars from AU+ mel-ko - always has a pile of proofs and nice ms state coins. smaller selection but hot coins. usually always has various franklins with fbls. zincled - honest and various selection. friendly and helpful too! arrowresale - doesn't always have a big coin selection but always has baseball cards. when they do have coins it is various but always something nice. i purchased a full eisenhower set from them in lots of each year and in ms/pr states with each mint mark. also got some nice mint + proof sets from them. coinsbybobby - got all my blue & brown ikes here in addition to a pile of mint + proof run sets. check this place out if you collect mint + proof sets and other things like silver eagles + eisenhowers.