iPhoto. It handles RAW, it does most of the editing you could want, and is cheap through the app store (I think £10). It does your cataloging and your editing.
If you feel the need to have brushes and a few more editing options then just go straight to aperture for £50. You can download a trial of A3 for 30 days free and see if it is for you. There is a slight learning curve, but nowhere even close to photoshop.
On a side note, does your forum name correspond to fly fishing?
Thanks,
Rick