A simple blue modification of the fantastic BlackMesa visualstyle, which can be found here:

[link]

Updated 6/6/2005: Added orange selection boxes for start menu, changed theme name in Appearance preference box to BlueMesa, and dropped saturation on the start button a little.
Updated again 6/6/2005: Fixed single pink pixel on start buttons.
Updated 7/6/2005: Added Tahoma substyles, shrunk start menu button area (Hopefully this fixes problems with French copies of Windows XP too.) Made Logoff button yellow.
Updated 8/6/2005: Fixed description text on start menu (now an attractive blue colour) and modified selection colour a little.

Permission:
This is the official resource kit for the Black Mesa visual style. Do what you want with it, my only request is that if you use these files in any other VS, skin, or website, you give me credit. No prior permission is required.

So if you feel so inclined as to make a wonderful modification to the Black Mesa VS, feel free to use these as you see fit, and release it at will!