Update from E6750

You will need a new motherboard.

What is your budget? The best processor that is supported by that motherboard is the Core™ 2 Extreme QX9650 but at $900+ for new, I don't really consider that reasonable. Actually, what I did find in the Q/QX series that were "reasonable" were used for $150-$250 on Ebay - I prefer to purchase processors new.
Here's what I did to find that. At the Gigabyte website for your motherboard, they have a processor support list. All of the processors on that list that do not have an N/A in the "since BIOS" column will work with your motherboard. Copy the processor you're interested in, paste it in your favorite search engine, see what you come up with.
Good luck

Did the same thing you did about a year back, trust me getting a new mobo will be money well spent, dont bother getting a new cpu for a LGA 775 board.
Since its a P31 chipset the best cpu would be an E8600 (depending on bios, etc) since quad cores aren't supported on P31 mobo's (trust me i learned the hard way....)

here is a list of cpu's your mobo can (depending on bios) support: http://ark.intel.com/products/33041/Intel-82P31-Memory-...
(click on compatible products on the left side)

Thanks everyone for helping, i've decided to buy a new mobo too then.

Remember you'll have to re-install windows and possibly upgrade from DDR2 to DDR3

An i3, 8GB of DDR3, and a Pro3 mobo will run you $210-$220.

Get an i5 2310


The i3's Hyperthreading makes no difference in gaming and the price difference between a i5 and it is really worth it.

When the heck did i3s get hyper threading?  

From worst and least expensive to best and most expensive:
i3
i5
i7

i3's have always had HTT.

My bad then. Thought only i7s had HTT. I guess the performance boost isn't as much as it is for i7s?