VHDL IDE for a GNU/linux environment
Both Xilinx ISE and Altera Quartus II IDEs run under Linux. Free downloads are available:

http://www.xilinx.com/products/design-tools/ise-design-suite/ise-webpack.htm

https://www.altera.com/download/software/quartus-ii-we

There is also Symphony EDA:

http://www.symphonyeda.com/

which might be better if you don't need synthesis. It's a nice piece of software. The free version might be adequate.