There is another type besides those already mentioned nl AST or acoustic soundboard transducer. My favourites of those are Baggs' I beam, B-Band's AST and K&K's Trinity Pure mini's. They comprise of 3 button-like Piezo's that are glued to the bridge plate inside the guitar similar to Taylor's Expression system. I like these because it is a straight forward no-nonsense plug-and-play setup.
My answer to your question though Norio, is microphones. It is no secret that for recording mics cover all the frequencies that an acoustic can deliver most accurately.
Since you mentioned that you don't want to go the sound-proofing route required for external mics, internal is my advice.
All the major pickup manufacturers have them available as combo's. I had a guitar with Fishman's Elipse Matrix blend system that was simply awesome, plugged in and recording. It is a combo of a mic and UST, with a soundhole operated preamp. It sells in the US for around $230.
Baggs's latest model in a Mic/UST combo, the "Anthem" gets rave reviews, and has excellent noise cancelling and feedback resistance features - it sells for $300.
They also have an older but very nice and reliable Mic/UST dual source system for $210.
Another brand that is famous for their mics/UST systems, is Highlander. They are expensive though.
A good solution for you might be a SEYMOUR DUNCAN's SA-6 MAG/MIC SOUNDHOLE PICKUP. It is also very affordable at $230. Magnetic pickups will only work with steel string guitars though.
These can all be viewed at Elderly's pages:
http://elderly.com/new_instruments/cats/PUA.htm
A good web site to read some reviews with sound clips, is Doug Young's -
http://www.dougyoungguitar.com/pickuptests/
The Aura acoustic image modeling systems from Fishman are apparently very good as well (from reading write-ups and reviews) - these have only got UST's (no mics).