For a quickie Ableton Live 8 tip, check out this powerful combo: Arpeggiator and Drum Rack.
Simply drop, for example, an instance of Live's 808 Drum Machine preset for Drum Rack into a new MIDI Track.
Then, drag over an Arpeggiator from the MIDI Devices folder, and drop it in-line just before the Drum Rack.
Next, double-click in a Clip Slot on this MIDI Track to create a new one-bar Clip. Simply draw in notes all the way across on the pads you want to hear; choose 3 or 4 (the piano roll view will tell you the Pad's "name" on the left-hand side). Now, trigger the Clip and listen as the Arpeggiator creates a drum pattern for you.
Go to the Style dropdown on the Arpeggiator device, and surf through the 18 options to hear all of the different patterns; use the Gate, Decay, Groove and Distance controls to fine-tune the performance. Try using different sounds and different numbers of simultaneous notes. For example, choose 5 for more complicated results or 2 for making simple house kick or hi-hat patterns.
This is a great way to quickly get solid main beats or backing percussion elements. To get even more crazy, try this technique with something besides drum sounds. Vocal phrases? Look out!