The one that seems to get the most talk around here is will the wii set the record for the highest selling system; I'll leave that one alone and give you some records that should easily fall.
Most sales by a 2nd place system: currently held by N64 (33 mil)
Most sales by a 3rd place system; currently held by GC (22 mil)
Most combines sales in a gen; currently held by gen 6 (180mil).
This means that potentially the top three spots and the combined total may all be owned by gen 7. Of course, later spots should be safe including top sales by a fourth place system (DC - 11mil) and top sales by a fiftth place system (Jaguar - 250k)