We are going to be in the Fort Collins, CO area for a couple months this summer. Would appreciate some see & do suggestions. We've will do Estes Park, but would appreciate some of the finer tips on it.

I would suggest that you make a day trip (or a couple of days if you don't mind dry camping) to Blackhawk, CO. It's an old mining town that is fueled by the casino industry. Still plenty of history and a gold mine to tour. It's up about 9,000 feet so it's a good hot day getaway. Golden, CO is also a very nice town and a tour of the Coors plant is available. Got a couple of extra days? Head across the hill West of Denver to Glenwood Springs. Good camping there at the No Name exit and the hot springs are one of the best I have ever visited.

If you're into fly fishing, Kirk's Fly Shop has great guided day fishing trips in the Estes Park area and they have reasonable rates. Take the Trailridge road drive over the continental divide. There's a train loop from Georgtown to Silver Plume with a stop to see a mine (1 hr trip). Georgetown is a great place to shop. Idaho Springs has the Argo Gold Mine tour, and of course lots of hiking and fishing in Rocky Mountain National Park.

Although it is a bit of a hike from Ft. Collins, if you miss the Pikes Peak region you are missing a lot. Such as Pikes Peak, Garden of the Gods, Manitou Springs, Cave of the Winds, 7 Falls, Woodland Park, Cripple Creek, Canon City, Royal Gorge, and the list goes on and on.

I absolutely agree.  The first time we visited Cripple Creek, we knew nothing of the area but it was much cooler and that sounded pretty good.  We made a 1 week reservation and left 2 weeks later.  We could visit the Gorge from there as well.

You could spend all two months exploring Rocky Mtn National Park, and still not see half of it. lots of great hiking, scenic drives & wildlife.
On the north of Ft Collins, take a day trip up Poudre River Canyon (hwy 14).
If you're into rodeo & related western entertainment, the Cheyenne Frontier Days in late July is just a short hop north on I25.

We spend the summer in Woodland Park. Come visit if you are in the area. Diamond Campground.

Thanks folks for the suggestions. They are all on the list.