The thriftmac FTP client of choice has a nice Mac-like interface and can take on most jobs without any trouble. For those with heavy-duty demands, check out FileZilla below. Fugu is also quite good, but it’s limited to SFTP.
Open source FTP program good for those who prefer access to local files in the same window as remote files.
OneButton FTP was kicked off the thriftmac island recently during Mac Freeware Survivor. But it has been updated for Leopard, and still gets many downloads, so it’s back in the collection.
Add a command to contextual menus so you can upload files from the Finder via FTP. Supports shortcuts, and more features may be on the way.