If you own Doom 3 you can download the Classic Doom mod, which will eventually be a total port of the original Doom in the new Doom 3 engine. It looks superb.
Other than that, try that underdogs website, failing that the "collectors edition" of Doom, Doom 2 and Final Doom is on amazon.co.uk for about £7, off the marketplace sellers.
It's also on amazon.com if you're in the states but it's a bit more expensive there.
Just because id hasn't stopped selling the original Doom doesn't mean they haven't given it to public domain, open-source, or other similar channels. Doom has actually been released via GPL way back in 1997 ... yet they still sell it. The same has just recently been done to Quake 3. I'm guessing you can go download the source and create original Doom since no one seems to provide any compiled version.
I'm guessing they are probably charging for the ammm ... materials. :laugh:
Source and the compiled game are completely different. Compiling the source would leave you with no levels, textures, or anything like that. So while the source has been released for many IDSoftware games, that doesn't make them free, it simply gives developers the chance to use the source for their own games and mods.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS