FPGA development kit for beginners , Spartan6 or Spartan3?
It looks to me like you still get a lot more to play with at a lower price point with Spartan-3. I found three different Spartan-6 options:


Avnet Spartan-6 LX16 evaluation kit, $225
Spartan-6 SP601 evaluation kit, $249 (limited time offer)
Digilent Atlys, \$199 academic or $349


Of note here is that only the Atlys has a lot of on-board common I/O connectors, such as audio, video and keyboard. The LX16 kit has most of the interesting details on a Cypress PSoC instead, though it features a battery that may be interesting. 

It boils down to what your intended projects are. With the lower budget Spartan-6 boards, you get an FMC-LPC connector that you can attach your own builds to; the LX16 kit also has a pin header, which is easier to get connectors for. 

With the Spartan-3 kits, such as I have, we have a quite varied set of connections of more limited quality, and for major expansion there's the Hirose FX2 connector (again, somewhat unusual). 

If your plan is to do video processing, I'd be very tempted to save up the extra money for the Atlys. It doesn't have very many expansion pins, but it has multiple on-board HDMI ports.