The Bridgestone Potenza RE050 and Potenza RE050A have been superseded by the Potenza S001. The Japanese website shows they make them in suitable sizes for the GTI, but unfortunately not all sizes are brought into the UK/EU market.
Best road tyre would be Michelin Pilot Sport 2 or Pirelli P Zero (not "P Zero Nero", "P Zero Rosso" or "P Zero System" which are old designs) for dry performance. PS2 is comparatively more quiet and comfy, but P Zero has better wet performance.
Otherwise, Michelin Pilot Sport 3 or Goodyear Eagle F1 Asymmetric for balanced performance (what little they lose in the dry they make up for in the wet). Continental SportContact 3 is also on par with these two, but is due to be replaced by the SportContact 5 (official launch is Spring 2011, however certain sizes are already appearing on the market). Should be interesting to see what improvements have been made on what is an already competitive tyre.
Recommendations are based on the assumption you're on 17's or 18's, and that you're not after track tyres or winter tyres.