I've gotten *really* into light nightgowns and chemises recently, especially as it starts to get a little warmer. There's something so easy and yet pretty about them. I definitely still sleep in old soccer t-shirts sometimes, but less and less as time goes on.
I recently bought one like this one, by Gilligan and O'Malley, at Target (mine's in a bright summery aqua, or calypso-like green, but they didn't have that color online). It's (surprisingly?) extraordinarily comfortable, light, soft, simple. It's also just pretty, and even a little sexy. And, come on, $20. Can't be beat.