One of the new features in Ableton Live 8 is the ability to step-sequence in the Midi Note Editor. This is covered only briefly on age 204 of the manual so I put together a 5 min. video tutorial to help you get your mind around how this feature works.
Update: I've gotten a lot of comments that people like this video but they feel this implementation leaves something to be desired. I want to mention that the upcoming add-on Max for Live has an "off the hook" step sequencer device. Check out more here.
I also want to point that that there is utility in the feature set shown here especially for step-sequencing chord structures.