It seems like the market is really pushing toward SLI. The only motherboards that don't support SLI seem to be HTPC oriented, which makes a gaming pc built from one a little less capable, it seems. I'm having trouble finding a good, reliable single video card motherboard. I'm wondering if I should spring for a gaming-oriented SLI board and leave the extra slot dormant? Seems kind of wasteful to me... but back when SLI first came out, the extra PCI-E slot shot the price of the board way up. ...doesn't seem to be the case now.

I'm not sure what to do. Here's what I'm planning on putting together...

2.6 ghz brisbane AMD X2 5000+ (preferably black edition to overclock to 3.0ghz)
2gb DDR2 (preferably 1066) with availability to upgrade to 4gb (4-240pin slots necessary)

I'll be transplanting over my current 8600gt and 450w PSU (i'll have to upgrade that sometime too).

Check out the K9A2 Platinum. When you have some more money and want a serious gaming PC, add two HD 4850 cards. For the PSU, the 750TX is probably the best choice here.

Check out the Asus M2N-E motherboard. It supports up to a Phenom X4 9650 and 8GB DDR2 800.

I don't mean to be rude, but I don't see how that's a good choice at all. You must be mistaken because the M2N-E doesn't support phenom series processors. It also doesn't have pci-e 2.0 or support AM2+, a necessity for longevity. For the same price range, I can get my hands on a whole list of other msi, gigabyte, and asus boards that have those things. I'm looking for something that I won't have to replace soon.

My opinion on SLI is that I'll be more likely to upgrade to a newer/better card than to double up. I'm a casual gamer and I'm looking to spend less than $120 on a mobo.

After a bit more research, I managed to stumble across these three boards...

(newegg compare link) http://www.newegg.com/Product/Prod [...] 6813128335

GIGABYTE GA-MA78G-DS3H
ASUS M3N78 PRO
ASUS M3A-H

They all run 700-series chipsets, support AM2+, DDR2 1066/800/etc, PCI-E x16 2.0, and in theory support the new 140W processors. I've read about some bios updates needed to ensure full compatibility, but I don't plan on moving on to triple or quad core for quite a while. I'm leaning toward the M3A-H but I'm looking for some input. I know they're not SLI, but my dilemma is whether or not I should include those boards in my choices. If someone can convince me that SLI is really the way to go, I'll definitely consider it.

Of those 3, I'd eliminate the M3N78 because it's the most expensive and because it has 10 times fewer reviews than the other two. OK, this is not a scientific method, but still, if only 7 people out of 145 bought it, it's probably not the best. I'm also worried about the recent bad news about nVidia chipsets. Stick with the 780G, it's safer.

Of the remaining ones, the Asus has 3 PCI slots, which is nice. The Gigabyte has support for 16GB of RAM, which is much less useful. Apart from that they're very much the same. I'd pick the M3A-H.

Actually the MS2-E DOES support Phenom processors with the latest BIOS 1401 up to the 9850 as outlined on the Asus website.

http://support.asus.com/cpusupport [...] 2N-E%20SLI

And since it supports those processors that makes it an AM2+ motherboard. This board was made before the Phenom was manufactured so support wasn't in the original description. It won't support the 140W 9950BE but if you look around there aren't many motherboards that do right now. Many are still testing for compatibility with that processor. I'm looking for one myself right now.

This board has a single PCI-E 16X slot and yes its not 2.0 but you didn't specify in original post.

Just my 2 cents on PCI-E 2.0: it's not really necessary for 8600GT or anything up to HD 3870 or 9800GTX. It does matter for HD 4850 or 9800GX2 or higher, especially for Crossfire/SLI configurations.