Thought maybe a listing would help for long-term referencing. Please edit as needed.
Existing Proposals
CAP's
Park and Open Space Plan (which includes the Greenline and Capital Gateway Mall)
Beltline & Parks
Mims Park
Downtown Streetcar
Multi-modal Station
Established Visions
CAP's Connector makeover
Expanded rail service
Other Ideas
The Big Lid (covering the connector with parks)
Give Olympic Cauldron nicer space or move to Centennial Park
Greenway linking Grant Park to Piedmont Park
Relocate Southern Railway Museum (MARTA accessible; Possibly overlook rail yard)
New/redone/clustered museums and attractions
Bring ATL Farmers Market into city
A permanent, midway-like space (Navy Pier) (Would be good next to Farmer's Market)
Atlanta Spire (ASpire!) Something akin to CN Tower