Look only at the latest chipsets and choose one with the features you want.

The rest will follow.

Narrow it down to a few boards and then google up some reviews and user comments.   

Here is an example of an nForce4 SLI board. The SLI gives the option of having 2 graphics cards in a PCIe bus.

http://www.msi.com.tw/html/newsrelease/media_news/20050301003.htm

Personally, I feel as if SLI is a sales gimmick aimed at fat wallets.

Other than that, the chipset is commendable.

Here we see an nForce4 board with a single PCIe graphics slot.

http://www.i-tech.com.au/products/7872_Gigabyte_GA_K8NXP_9_S939__ATX__FSB2000.as...

Here is a recent VIA chipset based board with a single PCIe x16 graphics card slot.

http://www.ninjalane.com/display.aspx?docname=sl-k890pro-939&page=1#top


Here you'll find a fine example of an nForce3 Ultra chipset based board with AGP graphics.

http://www.giga-byte.com/MotherBoard/Products/Products_GA-K8NSNXP-939.htm

An article on yet another modern chipset (last page summation):

http://www.tomshardware.com/motherboard/20040420/nforce3_250gb-25.html

Yes, it is a little confusing but you will need to make a couple of fundamental choices that will narrow your options.

First, you need to choose a SOCKET for your CPU.
The AMD choice is 754 or 939 pin sockets, the 939 being the more powerful (in theory) of the two. I believe the socket 939 will be better supported in the future.

Socket type can drastically affect the feature set of the mainboards, even within the same chipset. For instance, the socket 939 boards support onboard CPU memory controllers, dual channel RAM bus, and higher Front Side Bus speeds than the socket 754 counterparts.

Intel Sockets are not my  thing, there are some recent 64bit developments with Intel CPU's that look attractive, and their pricing is becoming more competitive. You are on your own here unless someone else can help.

Secondly, you need to choose whether you intend to remain with AGP graphics, or move on to PCI express.

Lastly, there is a quality and support consideration. There is nothing worse than a manual which is written in Pidgeon English from an obscure manufacturer.

While I credit any new or struggling manufacturer, it's safer to stick with known successful companies. Even some of these have only recent success.

Asus, Gigabyte, Soltek, DFI, Abit, MSI

Here is an example of what NOT to get....

http://www.gamedude.com.au/prod_show.php?art_no=mbASk8_combo_

That looks really cool and supports both socket types. Great Idea. Or is it? Asrock have stuck their neck out here in the hope of something innovative. (Read Gimmick)
It's what I call a "Transition Board" or "Combo" and you see them out whenever there is technology moving fast. This particular one uses an ALI chipset, which like SIS, (until recently) have not been very respected in the race for features and performance. This board could mean real trouble as far as compatibilty is concerned, I'm predicting blue screen city here. I hope I'm wrong.

I also hope this helps some of you become aware of what is behind a good simming PC.

Chipset matters.