Do Spanish speakers use the word "Tada!" or is there another, better one? I am particularly interested in Mexican Spanish. You use it when something is transformed or revealed. For example, when you reveal an unexpected gift, or when someone enters the kitchen you have unexpectedly cleaned.
For these cases in Spain we normally say... (hover over the block text to see it!)
You may hear it with a very long "a", as in "Tacháááááááán".
Since it is an onomatopoeia, it is not included in the RAE, so the source for the answer is my own memories together with this discussion in WordReference.
In Latin America apparently they use other variants:
The last is the one used in Mexico, as indicated by Flxtr in comments.
At least in Mexico it would probably would be ¡Tadá!, ¡Tarán! or ¡Tará!. Since it is not an official word, but a colloquialism, I guess it might change among regions.
In Mexico you say simply "tantán". You will not find it on any dictionary though. It is very smart from you to be interested in Mexican Spanish since it is the BEST Spanish out there. Your best source is Mexican TV shows from the early 90s and earlier. Back then, writers really cared about the language and very few mistakes were made. Nowadays TV shows are plagued with terrible errors. Still, it is much better than in any other Hispanic country, including Spain.