Are there any other good general purpose media players (ones that can play a wide range of formats, including DVDs) out there that allow you to advance or reverse frame by frame?

The only ones I know of are GOM Media Player and AVS DVD (the old version). GOM is awful at frame stepping though and tends to hang up (in Win 7 at least). AVS DVD is great at it, but the copy I have is several years old (the new version does not have it as far as I know), and it does not play some of the newer DVDs, I am guessing because their copy protection crap throws it off.