To be fair, TS mentioned that he doesn't want to hear the keys being pressed which I'd guess would rule any mechanical keyboards right out.
There are some mechanical switches that do not make noise. A friend of mine uses cherry mx reds and modded them with these rubber rings under them to reduce the sound of them bottoming out. The only real noise you hear in reds is the bottoming out of the keys. If the OP was interested, he could get Reds with the mod. Otherwise, go buy a dell membrane board for like 20 dollars. Unless you want some perks like backlit keys. It really all depends on what OP is looking for.