I love using OmniFocus to help me get stuff done, and I've been on a quest to find a good way to manage my References and organize my File System a bit better. I've tried TAGS from Gravity Apps and DevonThink, but recently, I've discovered Leap and Yep. The Tagging system uses OpenMeta, so a single Tag works in both apps, which I find to be nice.
I love how fast and fluid Leap is at looking @ my File structure and how it allows me to manage things via Tags and such.
Anyway, I thought you guys might like to check it out to see if it might fit into your GTD workflows.
If you use Tags, Yojimbo, DevonThink or any of the various other "Everything Box" apps, you might enjoy Leap. So far it's fitting in nicely with my OmniFocus workflow.
Have a look:
http://www.ironicsoftware.com/leap/index.html