Below are several market suggestions. I hope some of these are included, particularly short term ones with regular changing dynamics, so as to maintain an active community here.
Other suggestions for activity include creating an active reddit community and adding chatrooms to this website, but moving on to the market suggestions:
Question: "Will the Kansas State Legislature Raise Taxes in 2015?"
Relevant Link: http://www.kansascity.com/news/government-politics/article23256042.html
Question: "Will the State of Washington Raise the Legal Age for Tobacco to 19 in 2015?"
Relevant Link: http://www.theolympian.com/2015/06/07/3764093/vapor-product-tax-raising-smoking.html
Question: "Will Wisconsin increase nutrition assistance (food stamps) in 2015?"
Relevant Link: http://www.huffingtonpost.com/2015/06/06/food-stamp-cuts-wisconsin_n_7512392.html
Question: "Will the Federal Reserve Turn Over Documents to Congress Related to the Leak of Sensitive Market Information?"
Relevant Link: http://www.cnbc.com/id/102730152
Question: "Will Congress Pass Some Form of Police Reform in 2015?"
Relevant Link: http://www.theguardian.com/us-news/2015/jun/06/congress-police-reform-mandatory-killing-database
Question: "Will Congress Approve a Raise for Members of Congress and/or Congressional Staffers before the Next Term of Congress?"
Relevant Link: http://www.cnn.com/2015/05/19/politics/members-of-congress-pay-raise/
Question: "Will Congress Pass Gun Liability Insurance Requirements in 2015?"
Relevant Link: http://www.washingtontimes.com/news/2015/may/29/freedom-under-fire-congress-eyes-requiring-gun-lia/
I like police reform, but think it needs to be reworded/focused. Might include sentencing, or maybe prison/sentencing/parole is a separate market from police practices (like body cameras or even mandates to report or aggregate data better).
I like gun liability insurance, but also think that one might be better slightly broadened to general gun control (though I personally think insurance is one of the better policy moves we could make on the topic, for the purposes of a prediction market think action/inaction is a separate question from what specifically they are going to do. No reason you can't combine them into one market, but I personally prefer the simpler question that also happens to be closer to 50/50 chance today IMO (the other seems too much like, Congress will pass a gun control law, and that law will be liability insurance, and I'm not super ambitious about those odds.))