What CPU/video card is the best bang for the buck these days that I could upgrade, and would I need a new mobo to hold it? Also, would my power supply be able to handle the new i5, i7 processors and new vid cards? Also, what do you guys think about SSD hard drives, worth it? Necessary?
My Max spending limit would prob be around $600 budget, a little over is okay.
Any CPU upgrade would need a new motherboard (and RAM). Your PSU is perfectly fine for the mid-range cards, but not for the real high end GPU and Crossfire/SLI. An SSD isn't even in consideration with your current system. You have too many improvements that are needed before considering a high-end, high-priced, low-return part like a SSD.
Don't look at what's been selling the most. You're going to be looking at really old boards.
First thing you look at is the socket it uses. You should only be looking at Sandy Bridge CPUs (the new i5/i7, the ones with a 2xxx model number). All of them run on the LGA1155 socket.
Second, you look at the chipset. There are only two for the LGA1155 socket, the P67 and H67. The H67 will allow you to use Sandy Bridge's integrated graphics (more powerful onboard graphics), but won't let you overclock. If you weren't using a discrete GPU (which you will need to do), you'd want the H67. Otherwise, you want a P67 board.
After that, it's all about features. If you want the ability to SLI/Crossfire (use two GPUs as one, SLI is nVidia's tech, Crossfire is ATI's), you'll need two PCIe 2.0 slots running at at least 8x/8x. You can't really filter for this, so you've got to read the short descriptions. The other stuff is pretty standard, like how many SATA II/SATA III ports, USB 2/USB 3 ports, firewire ports, etc.
After you've got al the features you want narrowed down, it's all about the brands. You want a high quality board, so that eliminates several brands. I typically look for brands in this order: Asus or Gigabyte, ASRock, MSI, EVGA. Any other brand isn't worth it. Get whichever board fits your needs and your budget.
I tend to gravitate to ASRock more often these days for a few reasons. First, they're really cheap. They're typically $30-40 less than boards with similar major features (PCIe 2.0 slots, USB 3/SATA III support). Second, they're pretty high quality. Third, they've been winning recommendations and awards hand over fist. I can't think of a single ASRock model that Tom's (or someone else) has included in a review/comparison that didn't get a recommendation or beat the competition.