Well, I usually say "twenny" instead of "twenty" (not "twendy" even). I recently noticed that I never heard the same from any native english speakers during any talks I ever had with them.
Recently I had a brief search on the 'net and it seems that it is somehow okay to say "twenny", but it might look the least correct pronunciation for most of the people, or they might think you have strange accent, etc.
So, my question is, is there any good reference which clearly proves saying "twenny" instead of "twenty" is totally correct or wrong?
P.S. You're most welcome to write your very personal opinion if you don't know any good references.
Update
I've already looked at the major dictionaries and didn't find any of them lists "twenny" in their pronunciation's section, however I'm sure that I didn't made that up, but I heard that while ago. Maybe in a movie, maybe from someone, and that's why I'm looking for the answer.
Best Answer
The stop in syllables that end in a homorganic nasal-plus-stop cluster (in English, these clusters are /mb, mp, nd, nt, ŋɡ, ŋk/) is often elided. Word-final /-mb/ and /-ŋɡ/ never occur in Modern English, for example, although their dumb Middle English spellings hang around.
Final /-nd/ does occur, though not always, but it's frequently neutralized with /-nt/, especially after a stressed vowel and preceding an unstressed one. As in twenty.
This interacts with the neutralization of /d/ and /t/ in the same environment; in American English, both go to [ɾ], as in betting and bedding, which differ -- if at all -- only in the allophonic vowel length of stressed /ɛ/ in the first syllable of bedding.
Upshot: In American English, /'twəni/ is the normal pronunciation, /'twɛni/ is somewhat more formal and careful, and /'twɛnti/ is fastidiously careful.