Chris Pirillo asked his readers/ viewers what FTP clients they use. Like Chris, I'm a fan of WinSCP in Windows. I pretty much avoid unencrypted file transfers, if I can help it (I'd be more successful, if Windows Live Writer supported SFTP/SCP).
My Linux box, if involved, is almost always the server. I don't initiate file transfers with it, unless I'm downloading apps from the web via Firefox.
On my 4 month-old MacBook, uh, well, I've kind of stopped using it, so I don't remember what I installed on it. Don't you give me that look! The Mac has a keyboard and an annoying touchpad. I do digitizers. Give me a tablety Mac, and we'll talk. Anyway, I still carry the MacBook to work daily, just in case. As much as I spent for it, I'd better.
Er, back on topic. The one place I haven't gotten happily settled as far as the file transfer thing is my Sprint Mogul. My Linux machine has just about every decent Handheld PC and Pocket PC app I've ever found, and I would love to be able to grab some of those apps directly from my phone. Now, a lowly desktop support tech with a rarely used, relatively new MacBook isn't going to have a lot of dough, so I like my freeware. There is a ton of FTP freeware out there for Windows Mobile, but we're rather out of luck for secure putting and getting. There's a port of OpenSSH that also has SCP and SFTP, but command-line by thumb doesn't thrill me. I had resigned myself to dropping 20 bucks for zaSFTP, but when I couldn't even transfer one file with the trial version, I held off. That little trial expiration message might be by design, but I'm not going to pay $20 to find out it isn't. Basically, this means I'm not doing FTP on the PPC right now. I wish I were.