Citibank offers a lot of convenient services, including free online banking and bill pay, investment services, and of course 24hr ATMs. Whenever I've had to go inside the branch, the tellers were very efficient and friendly.
The one thing I don't like about Citibank is that they don't really have a good "free" checking account. In order to qualify for free checking, I think you need to maintain a minimum balance of $2500 or so, which is pretty high for some people. If you go with a checking account with no minimum balance requirement, you're limited as to the number of checks you can write each month.
Other than the minimum balance thing, however, I have no complaints about this bank.