CEX.IO was legit and the most known as far as I know , but they shutted down for someone because Bitcoin price dropped and it's not really profitable for them anymore . Also there is Bit-x I know that they do Bitcoin Mining , you should check my Signature for their link . and if you have further questions simply ask Marcotheminer here on their official thread : https://bitcointalk.org/index.php?topic=874312.0

~ Madness