With moving my workload to two laptops (one for work, on OS X and one for play, on Linux), you invariably have issues with being as productive as you should be in the software that you use. I dumped Apple Mail.app after about 2 weeks of solid usage (more on that, at another time), for Mozilla Thunderbird. It isn’t free of warts, but with the excellent plug-in architecture, it surely helps. Here are some plug-ins (add-ons in Mozilla speak) I can’t live without.
This tool is simply amazing. Ctrl+J for Junk, Y for moving to the archive, and so much more. Its keyboard shortcuts are similar to GMail, so if you also happen to use GMail, this is a worthy tool to have. Even if you don’t, the shortcuts make so much sense, its a wonder why its not on by default.