To throw in my two cents, I will also recommend eBird.
Some data can be seen, ie by searching Top 100 listers for a partcular area, or if one searches for a particular species in a particular area, a map of sightings will show up with notes as to who saw it and when.
Other than that, as previously mentioned, eBird reviewers will send requests for information to clarify exceptional sightings.
Among the things I like about eBird: I can view recent sightings for species I would like to see, I can build checklists for any area that exists within eBird using either my own sightings or all sightings, for the listing side, eBird provides an easy to use summary of species that I have seen in any major world region, any country, any province or state, and any county (which can also be a pain, I now have 1000 extra lists to build up!). Ebird does make trip planning a little easier.
The downside of eBird is that the beast works best when supplied with a constant diet of data and checklists.
If you want something low maintenance, www.bubo.org
is a listing site at its purest. All you do is create checklists for whatever area you like, and basically tick the birds off, with the option to add single sighting info. The downside of Bubo is that your information is public, and one can see a summary of where everyone's, say, Victoria Checklist or Canada Checklist is at. If you want that, then Bubo is quick and easy. Birds can also be added to multiple checklists as well. One other Bubo feature is the ability to generate a "target list", ie birds you haven't seen in a particular checklist area yet. This will also let you know how many, and what percentage of listers who have submitted lists for this area, have seen said species.
I use both (and also act as an eBird Regional Reviewer). My own reasoning for this is that eBird is the recipient of all detections, whereas on my "lifelists" I only count birds seen. Also, Bubo lets me build individual year lists with ease, and with a glance I can compare year lists from 2009, 2010, 2011, and 2012. From Bubo, lists can also be downloaded into Excel.
There you have it.