I got this...
http://www.topeak.com/products/detail/60
to go with...
http://www.topeak.com/products/detail/24
I ordered the specialized globe centrum sport which was said to have rack and fender braze-ons...which it did but didn't have the eyelets...doesn't make sense. I went with the seat post mounted one because I won't be hauling much weight and my bike doesn't have eyelets. I was using a backpack since december when I got the bike but just got the rack and trunk bag last week...my back thanks me.
Anyways, it doesn't spin on the seat post at all. It stays firmly in place. I switched out the quick release lever for a bolt to deter someone from stealing the rack...thanks to the brilliant mechanic that made the recommendation. It does sit up kind of high and you'll notice it when riding though. It's not horrible but does take a little getting used to. Overall, I like the setup because it reduces strain on my back and the quick release (for the bag) feature is convenient. The topeak bag is good quality, looks good and has good pockets, compartments, sleeves, etc. to make organization easy. Oh, the rack is the new home of my topeak mountain morph pump. I like it there better than on the bottom side of the down tube where it always got wet, icy or slushy on crappy days.
I called specialized after buying the rack above to see what the deal was about the lack of eyelets and they pointed me out to this.
http://www.axiomgear.com/product/rac...uct.php?id=138
It's adjustable which is cool but I don't know where it'd bolt to since there are no eyelets. I'll have to call them back and see what they had in mind.