I now have 3.
Pokerstars: By far my oldest active account, but I only play when I remember to register for the CC freerolls on weekends, so once every 2 or 3 weeks.
888: For just over 2 years now. I do virtually all my playing there now.
PlayNow: I actually created the account there 7 years ago,but there was no traffic at all then. I downloaded it again last night and it looks much better.
Full Tilt: This was the very first site I played, but around 2 1/2 years ago they "locked" my account and wanted me to send a bunch of info to get it re-opened. It was weird, I hadn't made a deposit or withdrawal on there in years and I had less than $2 on there and wasn't playing there at all. I just occasionally looked to see if there were any decent freerolls. I just couldn't be bothered to jump through hoops to restore an account that I wasn't even playing on so as far as I know it's still locked.