Supersprint fits 95% well but some of their slots are too long (I have one on my barchetta like that), but they are expensive. Not too loud and look good but it was a pig to fit, it took two of us 2 hours.
The three ITC we have fitted have been spot on - I have one on my Alfa 156 and it was fitted bang on in under 10 minutes (no I couldnt beleive that either!) It is no louder than the original at speed and just a little burble low down. It looks good too with the straight twin pipes and we sell them for a dmn fine rate .
There is a discount for BOO members of course. http://www.powerfiat.com/shop/index.php?cPath=8_9
You can get supersprint cheaper elsewhere as Tom will no doubt point out, but I cannot honestly remember the link lol (thats actually true, I was trying to!!)