The Tang Nano 9K is worth picking up for anyone who wants to play with FPGAs; it's pretty powerful for the price. The software requires you to apply for a free license, which they hand out like candy, but just plan to get hounded by sales guys for a month afterward.
My only real complaint is that the documentation is still a work in progress so you're going to be relying mostly on the example projects posted on GitHub.
(I should also point out that the Linux version of the software, like pretty much every vendor IDE I've used, takes some coaxing to get working on any even vaguely recent Linux distro.)
My personal favorite of the boards I've used is the TinyFPGA BX. It's about $40 and uses the fully open source IceStorm toolchain. They have decent resources, though I wish they had more available I/O pins. Still I managed to cram a decent CRTC into one including a 6502 bus interface.
For something beefier, the ULX3S is really nice, but we're talking about a big jump in price range (I think I paid about $150 for mine). For that price you get an order of magnitude more resources (both LUTs and I/O pins) and some useful built-in hardware like SDRAM and an HDMI-compatible port. It uses the Trellis toolchain, which is also open source, and shares a lot of its tooling with IceStorm.
In an ideal world I'd suggest the TinyFPGA as it's better supported and documented, but I don't think you'll find them in stock anywhere right now. In fact the Nano is probably the only thing not backordered these days.