I have a 10 month old, too. (She turned 10 months yesterday). Unlike her older sister, she has always been a pretty easy sleeper, and we have almost always put her down in her crib before she fell asleep, and she would usually just fall asleep without much fussing at all. However, just in the last few days, I have been having the same problem. She just learned to pull up (she's a little chunky, so I blame it on that...that it's hard to pull all that weight up). And now she stands up in her crib, and just screams at the top of her lungs. What I have been doing is at first, let her cry a little bit, to see if she will lie back down on her own (which she does know how to do, luckily). THen, if she keeps at it for a few minutes, and sounds like she is getting more worked up rather than calming herself down, I go back in there, I lie her back down, and I pat her back for a minute or two. I also give her a baby doll or stuffed animal to distract her. Then I leave. I had to do it about 2 times last night, but after that she stayed lying down, and in about 5-10 minutes she was out.
Like I said, she has usually been a pretty easy baby (especially compared to her sister), so I don't know if it will work or not. But even so, you might just try that...just going in and lying him down again and again, with a few minutes in between to see if he will just do it himself, and maybe eventually he will realize that he's got to lie down and go to sleep.
Good luck! I think sleep is by far one of the hardest issues as a mom, because you know they need it to be healthy, growing babies, but it's so hard sometimes to get them to fall asleep on their own. As someone else said, to keep in perspective, just remember that one day they will fall asleep on their own.