Great Event Websites - Not Specific to South Denver

Mile High on the Cheap - one of my personal favorites - sign up for their daily emails and receive 3-5 deals every day via email
Mile High City - On-line business and tourism guide for Denver area.
The Official site of Colorado Tourism - Events, Festivals, Restaurant Guide, Hotels, In state travel guide and more
Colorado Festival & Events Association - Calendar of Festivals and Events statewide
Arts to Zoo - Colorado's Guide to Cultural Events and Organizations

South Side Event Websites (now I am sharing my secrets)

South Suburban Parks and Recreation - Outdoor activities in local parks and sporting activities
State Park Activities Calendar - Chatfield, Roxborough, Cherry Creek and Castlewood Canyon
Arapahoe Park Horse Racing
South Metro Denver Chamber of Commerce
Arapahoe County Fairgrounds &  Regional Park
Arapahoe Library District
Douglas County Fairgrounds and Events Center
Douglas County Libraries

South Side City and Event Websites - by City

Aurora
Cherry Creek State Park

Englewood - city page
Englewood Parks & Recreation

Castle Rock - city page
Castle Rock Merchant's Association
Greater Castle Rock Art Guild
Castle Rock Chamber of Commerce Community Events Calendar

Centennial - city page (hopefully a work in progress)

Cherry Hills Village - city page (another work in progress, this link is to the parks and trail map)

Franktown
Castlewood Canyon State Park

Greenwood Village - city page

Highlands Ranch - city page calendar of events
Highlands Ranch Chamber of Commerce

Littleton - city page event calendar
Littleton Town Arts Center
Roxborough State Park
Chatfield State Park

Lone Tree - city page event calendar
Lone Tree Chamber of Commerce

Morrison - city page

Parker - city page event calendar
Parker Chamber of Commerce    
Parker Artists Guild
The Wildlife Experience

Sedalia
Cherokee Ranch & Castle