Some places to look for Mac games, which are actually not scarce:
http://macgamefiles.com
http://versiontracker.com
http://macupdate.com
http://insidemacgames.com
Also, many Mac mini-games are in the form of Dashboard widgets. Some sources:
http://www.apple.com/downloads/dashboard
http://www.dashboardwidgets.com
Last but not least, your Mac Book DOES have some 3D capability, and can even play fun titles like Unreal Tournament 2004 (my favorite--so many free add-ons it's like 1000 games in one) if you set the detail levels low. Casual 3D games should be fine too, plus Pangea's stuff (commercial games, but you can try before you buy):
http://www.pangeasoft.net
Games that are "Universal Binaries" (Intel-friendly) are preferred, but some games can be fine even without that.
The games you mention may run on Mac, but if they don't allow you to set the detail low enough... they'll run slowly. Game titles are more likely to run on the Intel integrated graphics if they don't use really high-end 3D. I doubt HL2 can be set low enough.
The real things lacking in the Mac game world, to my mind are: 1) racing games and 2) map editors. Both are rare. But the editor for UT2007 is planned for Mac
EDIT: Something a little different--and fun even if you don't choose to pay:
http://tqworld.com
Have fun!