Do I need SLI???

Well, in SLI, one gfx card controls half of the screen, the other, controls the other half, so you get higher fps. You should stick with 1 GFX card though, IMO.

Thanks for the help!

SLI is indeed 2 Nvidia graphic cards which work together to improve your framerates. Crossfire is 2 ATI cards. You have to make sure your motherboard has the correct corresponding chipset, each brand has it's own set of specifications to run 2 cards. You can't run Crossfire on a motherboard with an Nvidia chipset.
SLI is beneficial when you run games at very high resolution. If you run at 1280x1024 or less, you won't see much benefit from 2 cards. Also, a single high-end fast card is most of the time better than 2 cards in SLI or Crossfire of a slower version. SLI won't result in double the performance just because you have 2 cards. It depends on the game, some are better optimized for 2 cards than others. Normally, you will see an average of about 30% improvement. Some games will do way better, and some games actually run the same or even slightly worse than on a single card. Running 2 cards in my opinion works like this, you buy the best graphic card you can possibly afford at the time, you have to bite the bullet and go for the top dog. After 6 months to a year, you may feel you card is just not quite doing it with some of the newer games coming out, and by that time your high-end card has dropped in price a lot. So you grab a second one and presto! New found performance.
The other scenerio is you just have a ton of money to spend, so you buy 2 of the best cards out there and put them in right away. Remember, buying 2 midrange cards and putting them in SLI will not be as good a single high end card, and costs more.

For most purposes SLI(Nvidia) or Crossfire(ATI) is not worth the price for the performance gained.For example,2 7900gt's in SLI will get beat by a single 8800 series card with the 8800 costing less.Also 2 cards use more power.If you can get the second card free or dirt cheap then it is a little more attractive.

jitpublisher said it all

I am planning a new build too and was planning to go with an SLI based board. I want to get an 8800GTX so I was only going to get one in the beginning. But like jitpublisher said, down the road by adding a second card, you can increase your performance somewhat without having to upgrade your entire box.

With that said, I did a lot more research and now I am leaning towards a single-card board (P35) because I'm just not convinced SLI is worth it, even down the road. I still am on the fence a little, but as I said, starting to fall to the P35 side.

I've heard and read a lot of good things about the Gigabyte boards so I am leaning towards the GA-P35-DQ6.

Anybody out there convinced that SLI is "hands down" worth it?

I think jitpublisher pretty much nailed it on the head, but lets crunch it down. Should I get SLI? Simple answer, no. If you've got the money to spend without any worry then sure, go for it. But the average gamer, even the enthusiast really doesn't need SLI. I think it's more bragging rights than anything...

Thanks to all of you for the great advice. I was going to get my system this weekend but will now hold off until the July 22nd Intel price drop.

Plus it'll give me some more time to do some research on the P35 chipset.

  As an Sli user I can tell you that it does work and you don't have to use two top of the range cards although the better the cards the better the performance obviously, IMO you would be better off asking this question in the graphic card section and seeking responses from those who actually use Sli or Xfire rather than those who think they know whether its any use or not.  

I have used SLI & imo you are better off with 1 better card rather than 2 weaker unless you are running at least 1600x1200 with FSAA etc.

i have a sli motherboard but with one 7800gtx. For a 19" CRT monitor it is all i have needed. If you are getting a 25" monitor or greater I would get an sli mother board and see how one card handles it.