get some nice jcw alloys, you cant go wrong with those, or bullet alloys are nice.
best bet is ebay, there are always plenty of mini alloys going on there....take your pick. if you have a look in the gallery i am sure that you would get an idea of what they would look like on your car.
dont buy alloys that you couldnt buy from mini though. in my opinion it ruins the car. (plus if you get jcw alloys of ebay for 600quid then it looks like youve spent 1500 at mini....thus adding value to your car rather then taking it off with some aftermarket jobbies.