I hope this helps.
Trulia takes no responsibility for the rentals they post. You must do your homework and verify the legitimacy of the post and know that you are deling with the rightful owner. Never send money to someone you don't know. There have been rental scams perpetrated lately through Trulia, Craigslist and the other sites. Please be careful.
Your Castle Real Estate
I suggest you google "property management in Denver" and contact companies directly.
Housinghelpers.com is good but their inventory is very limited right now.
Craigslist is good too, but definitely has its fair share of scams.
Good luck to you!