I have played Guitar Hero 3 at 1280x800 and except for some parts like boss battles with Tom Morello and Slash, it tends to run well enough. Of course with physics not activated and with no crowd.
I also player just today Left for Dead ( a 2008 game) at 1024x600 at a playable frame rate (I didn't measure the number, just the playing experience I mean) with no AA o AF, all on medium settings of shadows and model detail, but there are some various combinations I still didn't try.
I was also able to play Dark Messiah of Might and Magic (which has sources engine as well ) and it plays fairly smooth to shoot and all with some settings at high and a few at medium, no AA at 1024x600.
I am still testing games like Race Driver Grid, which I tried with the Vista Home Basic my notebook came with and it barely handled the introduction and animated menu. Now I will test it on XP Pro and see what happens, but I am not hopeless at all.
I was very curious about some Need for Speed games, like MOst Wanted ( I've lost the disc so for now, not possible ) But I pretty much doubt I can play NFS ProStreet due to all the details and how it needs to have details or it's just awful to play on it.
I still didn't try any RTS game, but I already see World in Conflict is just an impossible dream for it.
I must make it clear that my notebook specs are:
Intel Dual Core T2390 (1.8Ghz, 1Mb cache, 533mhs FSB), 2Gb RAM, HDD Western Digital 160Gb 5400rpm and of course Geforce 8400m gs 128Mb)
I suspect the T2390 can be the reason of some lack of frames in some games (some physics here and there) but I am still checking all about it.