That said, WinCon is in two/three months! *squee!*
Coming from Colorado, I should probably warn everyone to bring snowy type clothes as well as warm. October in Denver means extremely temperamental weather. We could have dry roads and sun all the time or it could be a mini-blizzard one day and shining sun the next. At the very least, bring a lightweight sweater or jacket and at least one pair of jeans/slacks. There is a reason you don't find a lot of trick or treaters in revealing outfits on Halloween.
Adding to the weather, Colorado as a whole tends to be very windy. Basically, we could have blizzards, freak thunderstorms, or sunny sunny days. We won't really know until a few days before the Con starts. I will update everyone accordingly.
Another tidbit about Denver, it's not actually a mile-high, even though it's called the mile high city. It's close, I'll grant you that, but it's not a mile high. Ask Clex, she was in Denver twice in August 2008 and was also in my town that is actually higher in elevation than Denver by a couple hundred feet. It may just be me, but you can feel the difference in elevation.
Drink lots of water and keep in mind, especially if you're coming from sea-level or below sea level conditions, that you ARE going to a higher elevation and you WILL be in the Rocky Mountains. The air is more pure and clean but it is also thinner. You might feel a little nauseous, sleepy, or dizzy the first few hours, possibly the day, but that's relatively normal.
Obviously everyone's coming for the Con but Denver is gorgeous and there's a lot to do if you have the time. Unless you want to be propositioned, avoid Colfax if you can (its Denver's main prostitute street). Elitch Gardens used to be Six Flags and a day pass (that includes the adjacent water park), is $35 for adults but all but a select three/four rides are free. You also have the Denver Museum of Nature and Science which you can easily spend an entire day in and still not really see everything. Royal Gorge, the world's highest suspension bridge, is 2 hours away from Denver.
Tidbit: Denver had a theatre before it had a school or hospital!
Wicked will be at the Buell Theatre October 9th-11th (5 performances total that weekend). Tickets start at $35. Go here for more information and/or to reserve/buy tickets.
Colorado Springs is about an hour away from Denver and has, among many others, the Air Force Academy, Cheyenne Mountain (Stargate, anyone?), Garden of the Gods, and the Cave of Winds (I recommend the lantern tour).
This post is unflocked for WinCon uses if need be.