Building new gaming system, need suggestions on MB

Hi all, apologies if this has been dealt with before but I didn't see anything in the last 3 pages of threads.

I'm considering upgrading my current AGP/P4/DDR system for budget reasons, but I'm also mulling over the idea of starting from scratch.

The motherboard issue seems to have gotten more complex since I built my last machine 3 years ago, and so I'm having a tough time deciding on what to get.

I'm on a budget and cant' justify the $300 for a board. I'm looking for something around $100 or less that will give me good performance and reliability, without all the bells and whistles. My system is mostly used for games like Bioshock, NWN2, Oblivion, Call of Duty4, etc. so I need to have a strong system. I would like to go PCI-E for obvious reasons (though I hear people refer to PCI-E 2.0? should I consider whatever that is?)

Incidentally, what benefits do you get by spending a fortune on a MB? I would think your margin of return would be minimal - that extra money would probably be better off being put towards a beefier CPU or graphic's card, no?

Thanks in advance for any help!