Just thought I'd share what worked for my dd when she suddenly started to have sleep issues at bedtime...
She was a perfect sleeper since she was 6-8 weeks old (thanks BW) and suddenly, at 21 months, she would FREAK out when we put her down at night. The first few nights I ended up laying down on the floor in her room, it would take her up to 2 hours to fall asleep. Within days I was able to move to a chair, half inside and half outside her doorway. Dh and I would take turns. I finally decided enough was enough and started to leave the lights on low (dimmer switch) AND let her select 2 books to take to bed. As soon as we started this we no longer had to sit in her doorway, we would tell her that we would come back and check in on her after she was done reading. She would fall asleep within 10 minutes of "reading" to her dolls (at 8:10 sharp). So, for those of you having bedtime issues with an older toddler, it could be a new fear of the dark, just a thought.