Well... Here's my tops list:
32nd all the way out to golden. Stop at the brewery either pre or post look out mountain ride. (depending on your bravery)
There is a fun route through globeville. It's kind of nice in the evening when there isn't much in the way of traffic. I know that is a fav for our beloved Rival founders, as well as the Ruckus guys. Basically you leave one part of 38th st. and come out at another part of town like further down or something like fox and 42nd.
I do an occasional ride to boulder. Sheridan to 120th st, then to interlocken blvd. to coalton to McCaslin to south boulder road to broadway (boulder style)
If you want something for those not faint of heart, or scoot, Golden Gate Canyon is super cool! Probably something not for people with a 50cc. Golden Gate canyon is pretty much the 32nd ride, with a little jaunt up Ford to Golden Gate Canyon Rd.
I'm sure i have more that i am leaving out... Other than the obvious extended journey down to Colo Springs. Having done that ride i would recommend staying over night in the springs before coming back to denver. The full round trip wrecked my body and my wits.