I doubt that anyone here wants to do your shopping for you. What you need to do is get out a fresh pad of paper, sharpen your pencil, brew a fresh pot, and get to work!
It's best to start with the processor decision first, everything else will fall in line.
Your first decision is what level of performance you require (are you planning high CPU demand tasks like video editing?) and how much you want to "future proof" your purchase (trying to stay on the leading edge of the technology). Those are personal decisions.
You will find your best "bang for the buck" deals when buying a slightly older technology platform that provides the same or better performance as the (lower end) of the new technology platform.
This is a good resource for doing so:
Notebookcheck: Mobile Processors - Benchmarklist
(it includes desktop processors too) There are others.
Write down the model numbers of the processors that you are considering for your needed level of performance and then start online shopping. Write down the prices and compare. The decision will make itself.
In a nutshell, Intel's current technology is the Core i series, based on a new architecture different from the older Core 2 and lower lines.
The i7 line is on top: quad core, hyperthreaded (as Petey said)
The i5 line is mid-performance: Dual Core, Hyperthreaded.
The i3 line is low end, consumer grade - the new version of the "Celery" (Celeron). Dual core and "crippled".
As you will see from the above benchmarking chart, many Core 2 processors actually outperform the i3's and even some i5's. As do some of AMD's newer Phenom II's.
It's a little complicated, but just go at it and you will have your buying decision soon. Post what you are thinking of buying and then you will get some better responses and opinions!
Good Luck