I'm a big fan of whirlfloc, which goes in the boil with 15 minutes to go. Another couple of points for beer clarity- get a good hot break (kind of like when you cook spaghetti- big foamy head, then finally it stops doing that) and then chill the wort as quickly as you can, and get a good break. A good cold break will look terrible with lots of big gobs in it. But that coagulated protein is what can cause lack of clarity in the beer. If you get a good hot and cold break, you'll have less haze in your beer.
Another thing to consider is choice of yeast. Some strains, like the hefe mentioned above as well as some other strains (wyeast's German ale yeast, # 1007 for example) are noted to be poor flocculators, which mean the yeast tends to remain in suspension.
Cold crashing (putting the carboy in the fridge for a couple of days) can help with those stubborn yeast strains that don't want to flocculate.
Some yeast strains, like Nottingham, are noted for their particularly high flocculation rates and are very useful in helping to give the best clarity to the beer.