Keep in mind that there's is no such thing as
"free risk invesment", but you can always choose
the lower risks!
Here is a list of Low / Medium risks:

Low Risk: (All Paying - revised)
https://goo.gl/cyB2mt - HashOcean (Free 15KH/s) (review - check reviews)
https://goo.gl/Tyrj8E - BitsRapid (Free 15KH/s)
https://goo.gl/onbCiy - BitcoreMining (2days 50GH/s)
https://goo.gl/01l0aT - GenesisMining
https://goo.gl/6MzhbE - ZeusHash
https://goo.gl/iIkQsQ - Eobot
https://goo.gl/2xKFU8 - Coince
https://goo.gl/HeHXsg - OxBTC
https://goo.gl/gfoM71 - TopMine
https://goo.gl/7OJGir - BitcoMiner
https://goo.gl/1B8TbB - Hashflare
https://goo.gl/n431Jn - Otiis

Medium risk: (All Paying)
https://goo.gl/ztLQNp - BitStrategy (review - check reviews)
https://goo.gl/BQqHmT - GoodlyBit (review - check reviews)
https://goo.gl/hdVG4B - BitMinister (review - check reviews)

Reviews on face: https://goo.gl/BDjxFY
Blog reviews(ptbr): https://goo.gl/pvHBpr