I sometimes recommend vanguard.com, but only because you can get one of the best S&P500 index mutual funds (VFINX) from them without paying the transaction fee that other brokerages will charge you.
Not that I have an account there myself 😱 , I took a friend's advice when rolling over the 401k from my previous employer and put it at Schwab. I've been happy with the service at Schwab, but I can't recommend them unless you do have a big rollover or want to start a very well-funded general account.