There will likely never be a complete open source tool chain for FPGAs unless we manage to develop an open source FPGA architecture. The FPGA companies control the bitstream formats used to program their parts and they have onerous legal language in their user agreements that make it a rather dangerous proposition to try to develop open source tools by reverse engineering (nobody wants to lose their house).
The good news, though, is that many of the patents that protect FPGA architectures are expiring over the next few years. That could make it possible to develop an open source FPGA architecture. Of course, you’d need a few semiconductor companies to get on board and actually manufacture it…
As has been pointed out, there are free HDL simulation tools like Icarus Verilog and GHDL (a VHDL frontend for gcc). But all you can do with them is simulate your design to ensure that it’s functionally correct. You then need some sort of synthesis tool to take your HDL to gates and eventually to the bitstream. Xilinx and Altera have free web editions of such tools, but they are definitely not open source.