Two recommendations for you:

1. Lost Valley Ranch- 2 hrs southwest of Denver. I worked there for 5 years just after college, so I know this place well. The Foster family has been running this ranch for almost 50 years. An incredible place and amazing staff. The best horseback riding in the country- period. Hiking, fly fishing, tennis, swimming pool, skeet shooting. Plus a great kids program if you want to spend a week there in the summer. 

2. Vista Verde Ranch- just outside of Steamboat Springs in Colorado. This ranch is now run by two great friends, Ben Martin and Dace Starkweather. A Comprehensive experience with horseback riding, whitewater rafting, fly fishing, snow skiing (in the winter obviously), hiking and mountain biking. Beautiful setting and great amenities.

Both of these ranches are great for families, or for a getaway with your staff or friends. You can stay for a weekend, or for a week. Highly recommend either.