I watch that show "Super Nanny" and she has the greatest solution to this, and of course it's TV so it always works great for her. Anyway, she has the mom and dad put the toddler to bed, read a story, or whatever their routine is, then say good-night, give loves and walk out. If your toddler gets up, you are supposed to put them nicely right back into bed, say good-night, love you and walk out. If he keeps getting up, you keep putting him right back into bed, being very nice, but not saying anything to him other than "It's bedtime, goodnight. I love you." On the first night the parents usually have to put the toddler back into bed a few if not several times before they give up and go to sleep. Then the next night you do it again. Though on the second night the parents rarely have to put the toddler back more than once or twice. The theory here is that you are the one that is in charge, but you don't argue, or bargain, or get angry. It is bedtime and that is all there is to it. I know that this comes from a television show, but it worked for my friend. The trick is not to argue, plead, get mad, bargain, or anything. Just gently pick him back up, put him back to bed and say "It's bedtime now. Goodnight. I love you." When you are consistent with how you respond to him, he will figure out that you mean business. (You might have to keep the baby in your room until your 2 year-old is finally asleep)
I am a working mom of 5 children, ages 28 to 12, my 12 year-old is the only child left at home. I also have 5 grandchildren. I used a similar method to this one, but it took alot longer to work. This method looks like a tried and true one for me. If I was to have any more children (yikes!) this is the method I would use for my children.
Good luck to you! Let us know what worked for you and your son!