Trey has been pretty prolific with the solo albums. They all pretty much sound like Phish minus the other guys though (perhaps thats not too surprising). They're mostly more standard songwriting-based stuff rather than the more adventurous Phish material. Mostly decent but you'd still be better off with Phish's studio albums than with Trey's studio albums for the most part.
He's done some more experimental things here and there though. I really like his solo orchestrated version of Time Turns Elastic which is better than the Phish version IMO (that's my fave solo project of his, but I can't really consider it an album). A few of his solo tracks have popped up here and there on the recent Phish tours, usually to middling response, but sometimes they become highlights.
Mike Gordon's solo career is pretty similar. It's basically what Phish would sound like if he was the only guy calling the shots. Fishman and McConnell have done a bit of solo work too but don't really have proper solo careers.