I bought Optimal Layout from the App Store as soon as I saw it. The first version was okay, but the latest upgrade is absolutely fantastic. The ability to switch so quickly to different windows makes the app really worth it and I use the Divvy-like grid to re-size windows constantly in different Spaces.
Agreed, I've found it indispensable in my workflow. Handles spaces very well too, and works well with Parallels windows in Coherence mode. Plus the developer has been very responsive when I've brought up issues in earlier versions.
