Dear Tweeters,
Much useful information has been shared about the reporting of banded birds, in recent posts to Tweeters.
In my opinion, it would seem best to report banded birds directly to the Bird Banding Laboratory. That way, the information is put into the big database that they maintain, while still getting back to whichever local banding project is involved, whether it be an organization that traps and removes raptors from an airport, or a shorebird monitoring project, or whatever.
I just tested this out. I reported two sightings of a banded Trumpeter Swan. It was fairly easy. I typed the following into the search bar on my computer. 
www dot reportband dot gov
That brought me to the link below.
http://www.reportband.gov


>From there, it was simple to follow the prompts.

One caveat must be mentioned. The mapping feature on the Bird Banding Laboratory's website is cumbersome. It kept resizing and jumping around, and then would freeze for several minutes at a time. After about ten frustrating minutes, I gave up on the map and started over. 
Fortunately, the website does not require one to use the mapping feature. The two easiest alternatives are to give a street address, or to write a description of the site. I believe one can also submit latitude and longitude coordinates. 
A user survey came up during the process, and I wrote to the Lab, expressing my concerns about the mapping function. I hope they can improve it.
Even if you see only a number on a patagial (wing) tag or a neck band, the Lab can still figure out where the bird came from. That means that an observer does not have to go through the difficult process of reading a tiny aluminum leg band.
Two days after I reported the two sightings of that swan, I received two official certificates of appreciation in my in-box! 
Yours truly,
Gary Bletsch