I use the shock absorber ones and I think they're brilliant. Touch pricey but they do different levels of support which is good. i personally like mine not to budge (don't want to end up with spaniels ears!) so I use the highest impact.
I got mine pretty cheap of ebay. They are definately worth the investment and you will wonder how you ever managed without
My advice is don't buy cheap if you have big boobs. A decent sports bra is worth spending money on. I got my ones from Bravissimo which specialise in bigger boobies and are well worth a look.