Go for a star chart.Kids love it.It stops Jess straight away.
I will say we have to do it once evry 3/4 months or so whne she has a spate of coming into our bedroom and going straight off to sleep again when we put her back,about 4 times a night.
What I do is tell her the day before we are starting a star chart.If she stays in bed all night she gets a star and if she gets 5 stars in a row she can go to the toy shop and choose a small toy.If she gets out of bed she'll get a sad face on her chart.Then you'll have to start all over again with the 5 stars in a row.
(Make sense?)
When she gets a star I go really overboard with praise,if she gets a sad face,I just say never mind,maybe if you stay in bed tonight you'll get a star tomorrow.
You can do it with any stickers really.My friend has a ds and she uses tractor stickers instead of stars and barbie stickers instead of sad faces (he's so embarrassed)
we normally print one from
http://www.dltk.com