We are going through this with our 6 month old son also. Then it dawned on me, this kid needs more food!!! LOL, he's a BBIIGG boy for 6 months, and I guess I had forgotten since our last boy that cereal at night is mom's best friend! If you're not giving him cereal before bed, try it. If you are giving him cereal at night and he's still waking, then here are some other suggestions...
We play a cd all night long for our son. Helps him fall back asleep without us when he does wake.
We have also been back and forth with formulas for our youngest. He started waking when we went to the Similac Alimentum (Similac's version of the Nutramigen). We went back to Isomil and he slept like a baby. The hypoallergenic seemed much more dense to me, and may have been upsetting his tummy (could also have been a complete coincidence). We are trying to determine if he has a milk or protein allergy (bouts of mild eczema), but still have not quite nailed the culprit.
Mylicon drops are great if he seems gassy also. These were a God-send with our now 3 year old.
He's probably also teething. If all else fails, try some orajel and tylenol before bed.
Hard to nail it down at this age. Could be a million things. I'll think about you when I'm up with our little guy next time :) but hopefully the cereal will continue to work for us (and maybe for you, too!). Good luck to you, let me know if you find a secret!
~ V.