Awesome GTI have a good selection. You won't just get the pipe as they all come with a filter on the end.
I use the Neuspeed on my S3 running at 365bhp and 378 ft lbs.
Reasonably priced, well made and no fitting issues.
However, I have changed the filter included to this one and it gives at least 40% extra surface area for filtration. Maybe not needed though as the figures above were when using the standard Neuspeed cone filter.
You will need certain tools to do the job though as getting the turbo inlet pipe off is tricky along with removing the rear engine cover support bolts.