I've been using a program called Gamepedia on my Mac. It's pretty nice. The company behind it has other programs for keeping track of other collections like books and music too... I find it really easy to use and I like the layout.... I just need to take the time to use it .... so far I've only got my NES colleciton entered.
....now if only someone could make a plugin for it so it could search databases like digital Press, Atariage, NintendoAge, etc.... presently it only searches Amazon and MobyGames.
...they also have an app in the App store for iPhones and iPod Touches... which can sync with it..http://www.bruji.com/