Dude - I've done loads of research on tyres for my ST (waiting for my new Roc as I type!!!)
I swear by Bridgestones - I got more than 25k miles out of a set on the ST, they grip / corner really well and you can be really hard on em!
Check out http://www.tyre-shopper.co.uk/ts/search/SizeSearch.aspx" onclick="window.open(this.href);return false; - the online National Tyres and Exhausts site and you get a free tyre guarantee, which on the face of it looks worth having! £156 a tyre at the moment - not bad for 20k + miles.
Hope that helps!