another fun feature of renoise’s 256 segment cutup lattice (when you’re using the sample offset to do you slicing and dicing) is that you can switch out your beat with another one and still have something that sounds rhythmic and on beat.
Another vote for Rex.
And I’m just this minute going to register Renoise. 
Rex seems to be quiet interesting while SF2 is nice and easy. I used it with my AWE and BushTracker. But maybe a newer format should come with some needed basic and some enhanced features. Again I say somewhen, I don’t really need it in RNS 1.5 or what…
That’s two basic things, used in many synthesizers for example:
Velocity-to-CutOff (That’s when you touch a key softly and instead of a lower volume, you get a deeper CutOff or both together)
More samples for the same note (pressing softly -> Sample A, pressing hard -> Sample B )
That would be probably an enhanced thing :
Instrument Behavior (play different samples on a chord, different attacks on different velocity, change volume on aftertouch, porta to note while playing notes in legato)
I saw a thread about guitar emulators here. If we could make instruments with the features mentioned above, we’d never need these plugIns.
Furthermore we could share them freely, implement them in our songs release more source files instead of rendered songs.
…just some thoughts btw…