I'm a little surprised to see Radenight's card choices listed under "if gaming isn't a concern for you". The cards aren't top-of-the-line, but they're only a step or two below the best single GPU cards made by ATI or nVidia. I imagine that they'd be pretty good for gaming if your monitor isn't huge or you don't require too much in the antaliasing line.
In the ATI line, I've seen the HD4870 512MB version for less than $150 lately. The 4870 is like the 4850, but it uses GDDR5 RAM rather than GDDR3, for a significantly higher bandwidth. The 4890 is ATI's current best single GPU card, but I believe that it's not greatly superior to the 4870.
The nVidia GTX260 is similar to their best single GPU card (the GTX285), but it has 216 processor cores rather than 240. (There are also older versions of the GTX260 with 192 cores. I doubt they'd be enough cheaper to justify the lesser performance.) The standard for this card is 896MB of RAM.
The DX11 cards may be appearing soon, but I don't know about the release roadmap. ATI is supposed to be first out with their 58xx series, but I imagine that they'll first release a high-end model, to extract as much money as possible from those who want the latest and greatest.
My favorite spot to peruse graphics cards is
www.newegg.com. Their "power search" feature is particularly useful. I recommend using them as a resource even if you're outside their business area (US and Canada). If you can do business with them, their prices are pretty good. My only annoyance with them is that they charge the same for shipping for each item whether it is purchased separately or part of an order of many items. (That's partly because they ship from multiple warehouses. I've gotten stuff from CA and NJ.)