Well, nothing is free...except your operator's sms pc service. That's if it has one. The free sms sites now... You have to pay, one way or the other, and personally I'd rather give a dollar than become spammed, choked with ads, or have my privacy invaded. Looks like ZYB is the solution for me - not free, but cheap SMS, with answers back to PC or forwarded to my phone when I'm away.
PS: sms.ac is a scam! They've spammed all the people in my contact list with emails that looked like coming from me, which I never wrote, nor did I agree to.