Upgrading PC, what should I look for?

Howdy folks. I've been out of the hardware loop for a while and just need some advice. I'm looking to upgrade my motherboard, cpu, and memory.. most of my other components are fairly new but it's time to beef up the foundation.

This is what I currently have:

Intel Core 2 Duo @ 3.0 ghz
8 GB Kingston DDR 2
Evga Nforce 680i motherboard

I don't want to spend too much money, not looking for top of the line, just a noticeable improvement. Should I be looking at Intel or AMD? What's a good upgrade for me CPU wise (I know there are i5 i7 and such, but which is the best bang for buck?) and what are the good motherboard brands these days?

Thanks for your help.

will your power supply be sufficient? will the new power supply fit in the existing case? will you need more fans?
will they fit in the case?

stephen

Case is relatively new, screwless, plenty of room for everything. Power Supply is also relatively new, it's an 850W Corsair Gold Edition.

I am looking to build a budget gaming computer this is some of the stuff I am looking at. I am not an expert though lol.
cpu
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103872
mb
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157176
gpu
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161315