pivit.io - Nice iOS app, only binary outcomes, playmoney
intrade.com - The most notably prediction market so far, now back with Bitcoin betting
predictit.org - University project, limit to $800 per person per bet.
Augur, Ethereum prediction market
http://inklingmarkets.com/ - mainly focused on internal prediction market for companies
More here: https://angel.co/prediction-markets
List of betting exchanges:
Here's an actual trading platform for prediction markets:
PredictionMarkt — trading with Ethereum, supports short-sales through outcome bundles.