He won't stay in bed!

I'm in need of advice.

My son is 2.5.  We just made the big switch to a big boy bed for him.  The first night he did great- went to sleep fairly quickly and stayed in his bed all night.  Since then, it's been a nightmare.  He gets out of bed SO many times.  I'm spending and hour to two hours each night putting him back in his room and in his bed.  It's affecting his mood and temperament at this point as he's so irritable all day long (he's not getting enough sleep!). 

Anyone have any great ideas on how to keep him in his room and bed?