For you guys in the UK, M&S have a new range "Real Cool Cotton" that comes in keyhole boxer briefs, hipsters (no opening), keyhole briefs and slip (no opening).
They are lightweight but supportive, I especially like the boxer briefs, they hold my package in place without crushing. I like to lift everything up forwards when I pull my underpants up, I don't like it pushed down between my thighs, there's no room there!
A word of warning, though, I find I need hipsters and briefs a size larger than the boxer briefs - I haven't tried the slips yet.