This app was mentioned in 2 comments, with an average of 1.50 upvotes
I'm a fan of the Scosche Rhythm+. It's not a wrist one, per se, as it is intended to be placed on the forearm, near the elbow (although the review below mentioned that it also worked well when placed on the upper arm, above the bicep, which keeps it out of the way).
Review here: http://www.dcrainmaker.com/2014/05/scosche-antbluetooth-optical.html
Amazon link: http://amzn.com/B00JQHTJS2
As far as Android apps, I'm still looking for the best one, but for now, I'm using this: https://play.google.com/store/apps/details?id=com.ndevgroup.hrmonitor