Build in SL, via RL Apps
I found this shiny nugget via The Arch. This is a plugin for Maya, called SLTk Pro, then lets you export your creations directly to Second Life. You still must work with the SL prim set, but the plugin supports sculpted prims and sculptmap generation as well. Check out the video to see how it imports and sizes prims automatically in-world.
"SLTk Pro is designed for professional artists in order to apply their skills without any limitaion. Powerful functionalities of Maya can be utilized for object creation for Second Life, that brings maximum quality and enormous productivity gains to users."
Looks pretty dang spiffy, especially if you are already a Maya guru. The site mentions a 3D studio Max version as well. Check out the SIM tools website for more info. You can also see some samples in-world.