been thru this phase too... tried the not giving attention and putting her back in and it lasted for an hour and a half before i gave in and decided it wasn't the right strategy for her.... she thought it was a game and was thoroughly enjoying herself, minx!
its awful when you are going through it but it does eventually end... our rule is bedtime means going into your bedroom and not coming out... if she isn't tired i can't FORCE her to sleep, so she is allowed to read books in bed, play quietly (preferably in bed), or play on her little computer in bed etc.... but NO coming out of the room.... it took a while but works great now, and its also great for when you know you have put them to bed too early (for example they had a late nap or fell asleep in the car) - they can sit up in bed and amuse themselves until they are tired and you don't have to have them up with you in the evenings (my evenings are my sane time)...

she is now 3 and goes to bed beautifully... sometimes she protests and says she's not tired and doesn't want to go to bed, and we just say she doesn't have to, and put her in there and read her a story anyway and say night night, then its up to her.... 9 times out of 10 she will go to sleep, sometimes she will sing songs at top of her lungs until she is tired, but honestly she NEVER comes out.... and i was nearly pulling my hair out not that long ago as she would get up out of bed for up to 3 hours and i was at my wits end...

personally i think you have to pick a strategy and stick to it, ours has worked incredibly well for us, i see the super nanny working wonders with the no attention and straight back to bed theory.... i sort of think maybe stop messing around with different beds etc, i don't think its the actual bed she is sleeping in, she's more just going thru the stage they all go thru of testing boundaries at bedtime, i think the cot/bed/portacot/trundle bed thing might be irelevant and could be floating her boat in terms of her getting attention etc at bedtime, plus it might be a bit inconsistent if you want to come across in a no nonsense sort of way. just my thoughts... good luck, i don't envy you its the pits!!