Minimum graphics you'll need would be something like a 8600M GT/equivalent or better. So as a start, you need to be looking for one that has relatively OK to good graphics. The rest will be good enough. One can always upgrade RAM very cheaply these days, e.g. DDR2 sodimms @ Play click here (checking compatibilty at Crucial first click here).
List of laptop GPUs with benchmarks, etc click here.
Most laptops these days with good GPUs tend to have Blu-Ray drives & other stuff you may not need that only inflates the price. So I'd suggest also considering a refurbished/secondhand one with a good GPU. Possible places to look would be MCS click here, ACCW click here, ITC click here & NDC click here. G