Not too many 'starter' boards come with GbE (gigabit ethernet.) Off the top of my head, there is the Xilinx Spartan-3A/1800 DSP ($399 USD) and Xilinx Virtex4/FX-12 ML403 ($399 USD).
However, the Microblaze softcore CPU isn't fast enough to use GbE -- you can use the GbE link, but it'll run at 100Mbps or slower speeds. Therefore, you'll need a PowerPC based Xilinx FPGA board, such as the ML403/405.
If you can wait another few months, Xilinx's Virtex/5-FXT series is about to be released -- that's basically a Virtex-5 with embedded PowerPC 440.