When you read responses, please remember that what works for some babies doesn't work for all babies... Also, because your baby used to go to sleep on his own, but now won't, I'd look for the source of the problem.
First thought - is something scaring him in his room? At this age, for reasons unknown to me, my 1st son suddenly because scared of a stuffed giraffe that had been in his room since birth. When I took the giraffe out of the room, he started sleeping better again.
Did anything else in his life change - did he start daycare or switch childcare providers? Is he teething or going through a growth spurt? If it's any of these, he might just need time to adjust and get through this separation anxiety stage.
If you don't think it's anything like this, CIO can work, if your baby doesn't have any underlying issues, he is full and comfortable, and isn't very strong-willed. It didn't work for either of mine.
Child #1: very strong-willed. I tried CIO once and 2.5 hours into it he was still standing in his crib screaming, nowhere close to sleep. I gave up and went back to other methods - rocking him until he is very very sleepy then putting him in his bed a little more awake each night, until, over time, I could put him in bed fully awake and he would fall asleep on his own. It takes more time than CIO, but it can work.
Child #2: had reflux, woke at night to eat because it counteracts the acid from the reflux and makes him feel better. I continued to feed him at night 1) because I didn't think it was right to let him CIO when he was in pain and 2) all the spitting up with the reflux made it hard for him to gain weight and so I wanted him to eat as much as he could keep down. Now that he's outgrown the reflux (he's 16 months), I am using the method I used for my 1st to get him to sleep on his own and it's working. I am also giving him more food during the day, and am gradually switching him over from a bottle of formula at night to just water at night so that he becomes less dependent on the calories he gets at night (if you are breastfeeding, you can do the same thing by shortening the nursing session by a few minutes each week. The biggest trick to this is to NOT let him fall asleep nursing).
A third option is co-sleeping. I haven't done this, but you can find mommas who have, and it works well for them. They would be better at giving advice on this than I am, since I haven't done it.
Good books on helping your child sleep OTHER than Ferber's include Dr. Sears book and Elizabeth Pantley's book. Good luck!