Doom! Dooooom! In a browser! Yes! It's only the shareware chapter, and controls can't currently be rebound from their archaic cursor key default, but what a proof of concept it is. Browser X-Com next, please.
I believe the old man's been shoved rudely into Java or something before, but it's very much a different affair for this one, as it's realised in dripping-with-gaming-potential new Flash 10 format, thanks to Adobe's Alchemy project - which handily enables programmers to use C and C++ code. Which in turn means it's super-fast to load and run, dead pretty and should work on any browser/OS that Flash 10 plays nice with.
Oh, and a note on browser-Doom's origin. Literally seconds of research lead to me believe this originally cropped up over at Newgrounds, but it was GameKrunch that mailed me about their hosting it - so fair's fair link-wise, I guess. Or is it? I'm really not sure how this cross-pollination of Flash games across multiple portals works, or of the link-etiquette for it. In any case, the clever Flash-porter is definitely one 'Mike'. Thanks, Mike. Thike.