Because of the percentually high amount of students it means that, beside of having a large amount of beautiful/young people (yes you people wanting to see Holland for that!), a lot of vintage shops! So I will be as subjective as I can to show you the four that I find quite good:
It's like going into a timewarp being thrown back in the sixties! The entry has a plethora of dresses & playsuits and the other rooms have a variety of jeans, jackets & the likes. The shoes are well selected & I've been buying lots of those 70s style boots in 2008 when they were totally happening.
It's quite girly and frilly but that makes it good. The standard price for a dress is about 20 euros but they have a 10 euro rack outside too.
My last purchase from them is this playsuit: suited for floral play when the weather warms up.
Find them at the Voorstraat 48-50 in Utrecht or online.
People knowing Amsterdam will recognize it's name. It's the same store but I believe Utrecht is better organized than the two Amsterdam stores (although I like the one at the 9 Straatjes).
I think it's more of an eighties vintage store. They have lot's of jeans and quite a good selection of leather. I bought this leather/pleather maxi skirt over there for 35 euros. Not bad.
It's not exactly vintage, which will strike a bell with the connoisseurs, who know the difference between vintage & just really old clothes. Anyway, there are some gems to be found here between the 'just old clothes' and often under 10 euros. That makes it somewhat more satifying than browsing in the carefully selected vintage shop! They also have some fun boots for reasonable prices.
Find them @ Oudegracht 270 and read about their ideology online (only in Dutch)