amaroK 2 came out and has sucked in every major version I've used so far. If you can get the 1.5 version it's like the best music player I've ever used, but so far 2 has been so buggy and lacking in features that I haven't been able to stand using it. I've become a convert to Songbird, though, which I think is pretty great, but ymmv. I don't know about its monkey support though, I've never looked into it.

Filezilla is a great FTP program that supports SFTP.

Pidgin is pretty good, and the Linux versions just recently got voice and video support for XMPP (Google Chat basically). But if you need voice and video for anything else, well... there's Skype, I guess, which is hella outdated on Linux these days (though it still works). I think AMSN has some voice/video support though just for MSN.

Also, an addendum to Mike's thing about GTK/KDE: The Ubuntu package manager will automatically install any dependencies you need for apps so it's not a huge concern. The newest version (9.10) has a pretty awesome program manager, too, that makes it really easy to search for apps you might want. The only one I think I mentioned that (afaik) is not available in the Ubuntu repositories yet is Songbird, though you can find binaries for it without having to look too far.