Just to save you a bit of time ploughing through the search engines I've put my choice of top/recognised tuners for Audi's (VAG), and although originally was aimed at chip tuning encompasses general tuning as well, and does have a focus on the UK market;
Most recognised within the UK:
APR -
www.goapr.co.uk/dealer/index.html - Good maps and well respected, especially in the US. Just released OBD* tuning. Switchable options using cruise control.
REVO-
www.revotechnik.com/uk/ukrevo.html - Good maps, one of the first tuners to offer OBD* tuning in UK. Switchable options using switch (Dongle).
AmD -
www.auto-amd.com - More than just a chip tuner, they are a complete tuner unlike many others. Respect. New one-click system offers another option on tuning, by use of the OBD port.
Jabbasport -
www.jabbasport.com/Audi/Jabbachips/Contact/contact.html - For those that want to take their tuning that little bit further. Well respected.
Forge Motorsport -
www.forgemotorsport.co.uk - No chip tuning of their own but they do offer a number of great tuning products for VAG cars.
Star Performance -
www.starperformance.co.uk - APR dealers and tuners in their own right. Favoured by the boys 'North of The Border'.
Road and Sport Developments -
www.rsdcars-uk.co.uk/ - Oettinger dealer for the UK and also well respected for general tuning and styling options.
* - OBD = On Board Diagnostic. Tuning which is done via the diagnostic serial port located on the vehicle, so no chip replacement is required.
European VAG tuners:
Oettinger -
www.oettinger.de or
www.rsdcars-uk.co.uk/ (UK dealer) - One of the longest running tuners for Audi's. A great tuner with a great range of products.
ABT-
www.abtsportsline.co.uk/location.php3 - Again a long running tuner with good products. Official Audi chip tuning for The Netherlands, Germany and Belgium amongst other countries.
MTM-
www.mtm-online.de or
www.qstuning.com (UK dealer) - Well known for good maps with solid performance.
Projectzwo-
www.projektzwo.de or
www.roadandsport.co.uk (UK dealer) - Again a long runing tuner that's well respected.
SKN-
www.skn-tuning.com or contact SKN (UK) Ltd. on
www.scottsmototune.co.uk - Not so well known but good products nonetheless.
Upsolute -
www.upsolute.com - Austrian tuner, well known worldwide.
Other recognised tuners for chips mainly;
Superchips -
www.superchips.co.uk - Regarded as a general tuner offering nothing special, but map on 1.8T does produce good results!
Wetterauer -
www.wetterauer.de - Not so well known german tuner, but still heard of. Used in both the US and Europe.
DBM -
www.dbmengineering.nl - Similar to Jabbasport but in Holland. Nice product range with carbon air boxes. Produced a 420bhp S3 for the road!!
Bullpower -
www.bullpower.nl - Very little known about this tuner, but show good figures.
Sportec-
www.sportec.ch (Even though covered by AmD) - Relatively new to the UK scene. Good torque figures produced with the maps and satisfied customers.
Powerchips-
www.powerchipgroup.com - Hardly ever mentioned on the forums, like Superchips, but look to provide good results. The website is extremely good, and the detailed datasheets provided within minutes of an enquiry are full of info. Available through
www.mongooseexhausts.com or
www.motorsportworld.co.uk <http://www.motorsportworld.co.uk>