I figured that the bins the Legos were semi sorted into took up too much space in the larger bins so Ziploc bags were the way to go. The air could be pressed out of the bags before zipping them and then stacking them into the large bins....We did quite a big sort out a few years ago so we had a pretty good system already. The regular bricks were sorted by color, the little Lego men were sorted together with their hair-dos and outfits in one bin, the animals were in another etc. It was still a bit of a mess though and quite a lot was unsorted or just shoved in random plastic bags.
...now it was just a matter of getting the stuff out of those mixed bins and bags and sort those where they belonged. All the odd pieces (curved ones, printed ones, hinged ones etc etc) simply went into three large bags. Some sets that were already together in plastic bags were transferred to Ziplocs to keep them semi intact.
For full instructions and more photos, check out Organizing Wille's Legos on Chez Larsson. (Images: Benita of Chez Larsson)