I guess the question is how much do you want to spend? The possibilities are endless. However these I would think can be done for less than a grand:
K04 would be the obvious one, but then again you would want to change the rods for piece of mind to be honest, which is costly. Would need K04 manifold and downpipe, plus S3 fuel pump and injectors to make the best of it. Not that expensive when done, but then again, not that cheap either.
K03 hybrid would bolt straight on, but they are very expensive. If you are interested then give CR Turbos a bell, they will be able to give you some idea (
http://www.crturbos.co.uk/). Whilst this will be expensive, you *could* offset the cost of the hybrid turbo against what you then don't have to spend on manifolds, downpipes etc, as a hybrid will bolt straight on. You will more than likely need bigger injectors though to cope with the fuel demand. Also, a high flow exhaust manifold would be a good addition to this.
I had a K03-052 (K03S) on my AGU engine, with a manual boost contoller set to 15.5 PSI and a REVO stage 1 map. Went like hell in the night, although putting the power down was a struggle through the front wheels, even on 18"s. Was at least 220 BHP. I'd say if you're looking to get a bit more power without the cost, then fit a K03-051/52/53/58 (the K03S series) and get R Tech to map it. NOTE: You WILL need a Forge Turbo Intake Pipe for this.....
Assuming it is an AGU engine (you didn't say), R Tech have a special map which produces claimed 235+ BHP on a K03S. Failing that it is an AGU, you can just get your REVO map upgraded to Stage 2 for £50 quid.
If doing that you will deffo need one of these..
http://cgi.ebay.co.uk/NEW-AUDI-A3-A...arts_Vehicles_CarParts_SM?hash=item5636632a68. It's a really good kit for the money.