If you aren't looking to spend a lot for good quality then the popular low end IT-Zero "World's Lightest" bags from Landor-Hawa are not actually that bad a choice. They have a trolley roller frame that goes in the corners which gives you a nice large flat area to pack inside. The downside is that the handle is too wide to hang anything on -- that and the bags themselves are flimsy and cheap. But mine has done a surprising number of trips including being dragged up and down a lot of rough roads and is still going strong. I only have the carry-on model but it's been checked a few times. They're super popular in Ireland as they're inexpensive and let you make the most of the Ryanair luggage limits....