A user on Newegg's EggXpert hardware forum has posted a very useful chart
of all the modern Radeon cards broken down by price category first, and then generation (5850, 6870, etc) next.
The most helpful feature is that 5000-series cards are ranked next to 6000-series so you can see how they compare to each other. These cards are all ranked alongside nVidia cards for further reference.
It has helped me to understand just how screwed up AMD's naming scheme was for the 6000-series cards. It's not entirely accurate for our uses - for example, the 6000-series equivalent to a Radeon 5850, according to our charts at Mining Hardware Comparison
is the 6950 - a 1,100-bump-up in number. But the chart has the 5850 next to a 6850 <sigh>.
For reference, according to our charts here are the least and largest hashrates for each card:
Very interesting, huh.