I use Buzz and Buzé for the sound design possibilities from th their modular machine views. Some of their plugs still beat commercial VSTs for me. The peer controls ( plugins to control other plugins ) allow some nice generative stuff too. I'm also keeping an eye on Nakalyne and some of the other "buzz clones".
Milkytracker and Renoise for speed composing (Renosie when VSTis are needed of course)
I have an LSDJ cartridge, and I have the piggy on GP2x and an old GP32, but don't use either that much (yet?).
Milkytracker on Windows CE and Nitrotracker have featured on my commute.
I keep ReViSiT handy for projects based around MIDI/DAW softwares.