This mod has me drooling:
http://www.blackmesasource.com/flash/index.html
it i sthe ENTIRE original Half-Life completely redone in the new Source engine. Not like HL:Source which was the old game ported into the new engine, this is the entire game, from the gorund up, rebuilt in loving detail by a team of passionate HL fans who felt at least a little ripped off by HL: source.
Check out the site, these guys have some serious talen. The Garg model is nothing short of stellar.