I also miss Winamp (although not that much) and Miranda (IM client). When I'm on Linux I rather don't use any dedicated IM client at all. Just IRC + something web based.
As with text editor, I never used Notepad++ too much but at the moment I use Komodo Edit. It seems fine to me and it is cross platform.
Winamp? Bah, Foobar2000 is where it was at. Tiny resource usage, infinitely customizable, and an arcane UI. Switching to anything else feels like that cold, uneasy feeling you get when you run your favorite editor on a machine without your personal config file and try to use one of your custom keybindings.
As with text editor, I never used Notepad++ too much but at the moment I use Komodo Edit. It seems fine to me and it is cross platform.