student fpga kit
Xilinx has many nice development boards, but watch out for the USB port. It may only work for JTAG configuration, and not for general purpose USB communication. Check the specs.
Both of the boards mentioned by the original poster share this limitation: USB-port is for FPGA/flash configuration only.
An FPGA-board with a user-programmble USB-host/device controller costs more money, and those generally are targeted at the professional (not student) market. Tis means you give up a lot of example designs, solid documentation, etc.
The professional boards from Xilinx (ML40x, ML50x, Spartan 3A/DSP) all assume professional customers who know what they are doing.
The Spartan-3AN Starter Kit and Altera Cyclone-II 2C20 Starter Kits are excellent choices for beginners/students. I personally like the Cyclone-II Starter Kit a bit more, since it has more dip-switches and a bigger (4-char) LED display. Both of these are very helpful for beginners just getting started (later on, though they're mostly useless...) Unfortunately, it doesn't have an ethernet (10/100) jack.
The Spartan-3A/3AN Starter Kit(s) have an ethernet-jack, but unless you get the Xilinx EDK (another $495), you can't do much with it (unles you're willing to sit down and design your own Ethernet MAC.) And that Starter Kit's parallel-flash is only 4MB -- not really large enough to explore ucLinux. (The cheaper Startan-3E/500 and more expensive Spartan-3E/1600 kits have 16MB parallel-flash.)