Altera, www.altera.com has a version of their FPGA development software for Linux -- Quartus II. This tool allows FPGA development for many Altera eval boards, and is available for free via their website. My personal preference is to develop in Verilog rather than VHDL. The syntax is more familiar to someone who also develops firmware in C/C++. Overall, though this is a personal preference. Each language has its opponents/proponents.