As Carl points out below, the rental market is tight throughout the Denver area. So starting your search early is a good idea. I would suggest you check the usual websites (Craigslist, Trulia, Zillow, Padmapper, Hotpads, Realtor,com, etc.). But be careful. There are a lot of scammers using these sites. Especially, don't send money and don't look at rentals alone. And, as a general rule, don't get involved with anything that does not sound right.
You might also Google "property managers Denver" and start calling some of these folks. They may have nothing now. But if you call regularly and get to know them, they might be very helpful when the time comes. If there are apartment complexes you like, getting to know the managers at these can also be useful.
You should do your own research into neighborhoods. For good reason, real estate agents must be very careful about what we say. There are legal limits designed specifically to avoid what is known as "steering." But, legalities aside, you are asking for opinions that would be very subjective and, thus, probably not very useful.
I would suggest you start at Denver's website:
And the Visitor and Convention Bureau "about" page:
And then use Google to fill in the gaps.
Whatever the case, you've made a good decision in moving to Colorado. You're going to love it. And, if you are like most of us, you will never let anyone drag you away again.
Good luck with your search!