onshape.com

This is a new software product being developed by the people who built SolidWorks. It is a very comprehensive web-based 3D modeling program that is free for individual/non-commercial users but has a monthly fee for groups & companies. It has some of the intuitive drawing features of Sketchup but also lots of functiojality for making complex models comprised of multiple parts.

My own opinion is it is a bit over-powered for 3D printing, but if you stick with the more basic functions it works really well. Plus it provides great backup and no software on your PC.