You can lend your Bitcoins on several Bitcoin Exchanges to other traders for margin-trading or shorting – and you get quite nice returns for that, depending on how hot the markets are.
At the moment (4/30/2017), you can get up to 0.29% daily if you lend your bitcoin to other traders on platforms like bit mex or whaleclub.
Also other crypto currencies can be lent to others – ETH, DOGE LTC, STR, XRP – just to name a few.
Check out www.cryptolendingdashboard.com to find the current interest rates on one site.