There are two main vendors: Xilinx and Altera. Don't bother going to their websites, they only sell the latest and greatest directly (this will easily cost over $1000).

Instead, there are discount vendors that will sell older chips (generally 2-3 generations behind the curve) for cheap. The names to watch are Digilent for Xilinx and Terasic for Altera.

I tend to prefer Xilinx stuff. I don't really have the time to write a more detailed reply, but you can browse around here [1]. Get something with lots of ports, or you won't be able to make anything interesting without a lot of pain (where interesting means "I want to hear/see/communicate-to another-computer my results"). The Zynq boards also come with an ARM processor that can talk to the FPGA fabric.

[1]: http://www.digilentinc.com/Products/Catalog.cfm?NavPath=2,40...