IGX

Yojimbo: easy information manger for Mac

Absolutely effortless way to aggregate and dis-aggregate information.

Even if you are disciplined, you can’t really duplicate what this does with just the OS.

http://www.barebones.com/products/yojimbo/

I've heard that's real good. I use Soho Notes. I also have a demo of DevonThink which is is just insanely powerful. Their demo is cool too. Rather than giving you x number of days they give you 150 hours of use. Really enough time to get into it and see how it works.