I use an application in Windows called GAPA (Gamma Panel, available on Major Geeks, iirc) that lets you assign hotkey shortcuts for different hardware gamma levels. I use 4 shortcuts: Ctrl+Alt+Shift+1 is 'normal', with gamma and brightness at their default values, Ctrl+Alt+Shift+2 is 'brighter', 3 is 'very bright', and 4 is 'maxed out'. Setting r_gamma in Tremulous overrides or resets these, so I usually adjust r_gamma first, setting it to 2.7 or so, and then will typically use my very bright setting. Only on some very dark maps is my 'maxed out' setting needed, like for the ceiling in the window room on Niveus.