You may wish to consider QPict. It is an excellent viewer and organizer. I tried lots of them when I came to Mac (only a few months ago) and settled on this shareware item.
Go to
www.qpict.net
Qpict is shareware, not freeware, but in my opinion, more than worth it. Coming from Linux, I was adverse to paying for ANY software but I found QPict to be good enough to be worth paying for. It is now one of a very few paid applications I have purchased.
If you feel like installing Apple's X11, and then DarwinPorts, you can run two of the Open Source world's best alternative, F-Spot and DigiKam. Both are very, very good at this sort of thing. I bought QPict before I realized that DarwinPorts existed or else I might have done the same thing. Having paid for it now though, I use it vs. its Open Source equivalents.