Rain diverter designed for 2-5/8" square downspout. Diverts rain to rain barrel then bypasses when full. Mount output pipe just below the top of your barrel and it won't overfill (see horizontal line on my siding). Grating filters out larger leaves and debris. Diversion chamber drain holes are in the model to prevent freeze up and drain small grit. Plug them if you don't need them or feel there is too many.
A shorter pipe to the rain barrel is preferred (as opposed to mine in the picture).
For future improvement:
Bottom section should either be redesigned to fit inside the downspout or a 360 degree lip should be added to prevent water from running outside the downspout pipe. I used a ring of caulking which the lower pipe sealed against.

Update 03/2015: Survived the first winter!