2(x)ist and Jockey, with Hanes a distant third. (I can never get a pair of anything Hanes (except their baggiest boxers) to fit at all. Same for CK...I like their t-shirts (though they're to short...), don't like any of their underpants styles because they don't have enough room.
Surprisingly, JC Penney makes a nice crewneck t-shirt. Not the generic ones, but the more expensive Stafford Premium weight all-cotton...nice collar, not too loose or tight, not too narrow. Nice amount of room in the trunk, but snug enough to show off my pecs, and long enough so they don't gap and show off my underpants when I stretch.
Only thing I don't like about 'em is the sleeves are too long. They're elbow-length or so (too long to wear without showing under a short-sleeved shirt).
My perfect t-shirt has sleeves that are mid-bicep, so I can show off my trips to the gym without totally stripping off my t-shirt <g>, and so it's easy for my lover to slip her/his fingers up the sleeve to play with my collarbones and pecs while we're making out.