PLAY

Links to a series of articles on PLAY: A Playmaking Metric:
Part 1 - Introduction.  Defining marginal contribution

Part 2 - Altruistic contribution
Part 3 - PLAY, the playmaking metric

A link to the full paper can be found here.

Summary
PLAY is a metric for quantifying playmaking ability in hockey that is better than assists in two quantifiable ways: (1) it is more consistent than assists, and (2) it is better than assists at predicting future assists. 

Two main reasons for the improvement are:
1. It is uses both shots and goals. (Assists are based only on goals.)
2. It accounts for strength of teammates.   

See links above for more details.