Well there is Captains Scarlett's Pirate Booty and Mr Torgue's Campaign of Carnage so far. I think you should be in your 30's before you go into any of them, but i like to wait till you cap out to get better loot.
As for whats good, i disliked Mr Torgue's. The timed missions killed it for me.. but there is some funny missions and its still the same borderlands fun.
Yea but can't you do them twice? like once the first play through and again after you start over and keep leveling?