I love buying pre-cut fabric from ebay, send me a pm if you post yours there.
I like layer cakes, jelly rolls and 6" squares with a lot of variety.
for 6" squares I like to buy lots of 100+, I don't bother with smaller quantities.
But I also buy yardage and fat quarters if it is offered as a 'lot' with a bunch of different fabrics, especially if they coordinate.