A new graphics card is always in the top three PC upgrades (behind RAM and hard drives), and while some people are ready to put $500 down for a new graphics card, most want something a little more modest.
Enter the HD 6670.
The HD 6670 isn't a powerhouse GPU, and both AMD and NVIDIA have far more powerful silicon, but for $99 you get a GPU with 480 stream processors running at 800 MHz and a 128-bit memory bus, running at 1GHz (effectively 4GHz) hooked up to 1GB or memory. On the down side the HD 6670 only has 24 texture units and 8 ROPS (compared this to the 96 texture units and 32 ROPs on the HD 6970).
I like the HD 6670 cards because they're short cards (and thus easier to fit and don't block air flow), and since it draws all the power it requires from the PCI Express slot there's no need to hook it up to the PSU. One downside is that most HD 6670 cards take up two slots given the thickness of the card/heatsink/fan (exceptions are the XFX HD-667X-ZAF3 and XFX HD-667X-ZHF3) so take this into consideration.
If you're going to buy this card (or any card in the sub-$100 price point) then it's important to approach it with a reasonable expectations of what it can do. While you'll more than likely be able to crank up older games to the max in terms of graphics quality and still get the 30 FPS or above, with modern games you will need to pull the sliders down a bit (don't expect to play Crysis 2 with all the knobs turned up to 11!). Don't expect to be able to push 1920 x 1080 pixels through this card, but 1280 x 1024 should be OK with most titles.
So if you're looking for a sub-$100 graphics card for a general purpose PC that will also see some casual gaming, then the HD 6670 is well worth taking a look at.