Here\'s my setup
I use ir_black in Terminal.app but in 16 color mode, and it looks great. If you really prefer 256 color, I recommend iTerm2. The settings allow you to have the terminal report itself as "xterm-256" which is what's needed to use 256 colors in Vim.
Check this website for the procedure: http://kevin.colyar.net/2011/01/pretty-vim-color-schemes-in-iterm2
There is a ir_black-based Vim theme called tir_black which is better suited for 256 colors: http://www.vim.org/scripts/script.php?script_id=2777
Looks awesome!
iTerm2 also has loads of nifty features.
I hope this helps.