The Poudre has lots of excellent class III sections and is very accesible from Denver. It also has one of the best snowpacks in the state this year. If you can make it up to the canyon after work or on any weekend day you will find tons of people who would love to boat with you.
You will find most people interested in class III at bridges take out, a big parking lot about 4 miles into the canyon. Bridges is a fun and relatively safe section that is runnable at lower levels than the other sections of the canyon. It's a great place to get a feel for the nature of the river, and to see if you want to step it up to the more challenging runs up stream.
There is no accurate cfs gauge for the Poudre, and everything is based on the river level at a marker rock. You can sign up for daily rock reports at poudrerockreport.com. 1.5' is about as low as most people will go on the bridges section, at 2.5' all of the class III sections from Steven's Gulch Down are good to go, and at 3.5' and above everything starts to get really good and the upper canyon runs (Rustic runs) are worth a trip. In my opinion, more water is always better on the Poudre.