There are three large multipools:
middlecoin.com - does everything for you, converts all coins to BTC
hashco.ws - more configurable, allows you to specify which coins to convert to BTC and which to keep
multipool.us - no automatic conversion, but can autosend to crypsty and autosell there
You can also set up your own automated switching setup using MultiMiner:
https://bitcointalk.org/index.php?topic=248173.0That way you mine just the coins you want to, and can adjust the profitability weightings to bias in favour or against or certain coins.
This option gives you the most control, without needing to constantly check the profitability figures yourself, plus you do all of the pool configuration for each coin, so the process is much more transparent.