When you finally consider a Mac - Aperture is good. Previously I disliked it but hadn't given it a big enough run. It's a total mind change from the way you use a PC system though and once your ready to throw out your old PC ways of thinking about file and folder naming then Aperture is really the way to go. It has its own backup system called Vault which is a compressed archival system - it too works well. All the storage of your media is in an compressed archival system but you do have the ability to output a single or multiple image files in either the master (original file) or in a version (post processed file).
If you end up resisting the natural urge to move to Mac - try using Portfolio. Its purely an image management tool with a very good tagging system. Of the all the PC based DAM systems, Adobe Bridge is probably the best available but I think you have to purchase CS4 to get it.
With the Mac once you start with Aperture you lose the ability to use Bridge but can still use CS3 or 4 or what ever other processing software you wish to use. The limit is you can only specify one package to use in the software preferences.