I got a Nike one in the sale from www.wiggle.co.uk because as well as it being discounted, you can use a code from their home page, to get an extra 10% off for Fathers Day (YES even on a sports bra, lol).
It arrived today and I got some free haribo with it, lol.
Sports bras are usually graded by the amount of support they offer. Normally ranges from light (e.g. yoga, walking) to heavy (running etc)