Silo is by far my favorite modeling program for organic stuff Ive ever tried. The topology brush alone makes it worth having. The only thing silo is really lacking is uv tools but mabey in the next release they will add this feature. In the Next release of silo they are adding zbrush style sculpting tools so it will be even more powerfull. Best yet its cheap at $109.

If you are interested in modeling Hardsurface models such as buildings, Mechanical, exc... you may want to try Sketch up. It only has a few tools but the way it works is amaisingly fast and easy. It even does a pretty decent job of creating uvs automaticly.