I did a G45 build a couple of months ago (The Gigabyte GA-EG45M-DS2H), but in hindsight would probably have been better served with a G33 instead (Gigabyte GA-G33M-DS2R comes very highly recommended).
2 of the things you said are at odds with each other: PCI-E 2.0 and improved onboard video.
If you are going to do any gaming at all, get a discrete card, the Integrated Graphics aren't up to much over 2D work and movies (I've played H264 stuff with no problem, but can't comment on BluRay playback)
If you're going to get a discrete card, the more powerful card you get, the more heat you're going to have to deal with and that can get tricky in an mATX case.
In which case if you do decide to get a less grunty card like an 8800GT or 9600, do you really need PCIE-2.0?
If you're still reading at this point you might want to take a looksie at anandtech (not sure exactly how strict the rules are on linking), they have started a set of articles called "The IGP Chronicles" which gives a great comparison between the old and new chipsets and a rundown on the boards available.