I love Critters for sci-fi and fantasy. (I'm not sure how they are for other genres.) They're professionally orientated, mature, and give solid critiques that tend to be helpful (neither too soft nor so hard that you're like "OMG, why?!!" Although I've found that the hard ones are rarer than the soft ones.). They're definitely worth checking out. The only sad thing is that they're a little slow (i.e. it takes about four weeks for something to get through the que - not so good if you have a deadline!), their formatting gets wacky, and I've noticed that a lot of novels get very few critiques. (So if you go that route, I'd definitely recommend doing it only after establishing relationships by critiquing a lot of other stuff/submitting a few shorter pieces.)

If you do end up becoming active, you'll have to look me up. ;)