For most of my FTP needs, I've been using FileZilla. While convenient for most needs, the site manager becomes a bit bloated when more and more projects are added.
So I was curious:

What do you look for in a good FTP client? What clients would you recommend?

Bonus points for:

• Being available for both Mac and Windows.
• Being able to organise a larger number of sites or easily switch/search between them.