Pocket Informant is a lot more than a contact manager, but it does CM very well. I've been using it for a long time.
I've tried a lot of the others and keep coming back to this one. (The only other one I haven't tried is Sunnysoft, which looks pretty good. I used PhotoContactsPro for a while, but besides being a little large, it also seemed to have some conflicts with other software that I was running at the time.)
iContacts and PocketCM are good, if a little short on features- but you can't argue for the price (which is free right now).