Within that budget/TV size you will have to look secondhand, or LCD.
There is only one plasma I would consider buying new on a 500ish budget and that's the Panasonic 37PX80, so at 350 you are struggling. The older model 37PX70 was a good TV and you might get one second hand for 350ish. If looking secondhand then try and get one with some remaining of the 5yr transferable warranties as the PX70's had a possible 'line down screen' issue on one batch of TV's (not all...) and it's best to be covered.
Personally I would steer clear of Samsung and LG Plasmas as I've read reports of image retention and fizzy pictures etc, but I use my plasma for gaming as well.
IMO plasma certainly beats LCD for standard def tv, but it depends on the viewing distance. at 7ft+ then the blockiness and noise associated with LCD on standard def is almost unnoticable. I'd still choose LCD over plasma for gaming - avoiding the sets with reported lag of course.