Here are some sites that I find useful for animal ID, sighting contribution, and personal sighting stats.
Birds:
eBird
http://ebird.org/content/ebird/ Mammals, Reptiles, Amphibians:
Are there any?
Butterflies and Moths:
http://ebutterfly.ca/ - Like an "eBird for butterflies." Butterflies only, though they may eventually expand to moths. Accumulates sighting records. Tracks/displays personal stats. Shows range maps of submitted sightings. They are set up to provide IDs for unknown photographed species, but in practice they rarely check mine. They might be understaffed for IDs and still building a reviewer network, since they expanded from Canada to the US early this year.
BAMONA
http://www.butterfliesandmoths.org/ - Butterflies and moths. Excellent and timely with providing IDs. Accumulates sighting records. No personal stats. Shows range maps of submitted sightings. In my experience, the regional butterfly reviewers usually provide an ID in 1-3 weeks and the moth reviewer usually even sooner, often in 1-2 days. Provides rather incomplete county-level moth checklists with the upside that it's easy to submit first county records for lots of species. On the other hand, the county butterfly checklists are likely complete. A downside is the one-sighting-at-a-time submission form, though one of their developers told me that they are working on a solution for bulk sighting entry.
In practice, I use eButterfly for tracking personal sighting stats and BAMONA for IDs.
Dragonflies and Damselflies:
http://www.odonatacentral.org/ - Shows range maps of submitted sightings and checks species ID of submitted photo sightings. Shows complete county checklists and accumulates sightings. Provides an online field guide.
Insects and spiders:
http://bugguide.net/node/view/15740 - BugGuide has a useful and extensive photo guide and provides crowd-sourced IDs, some from experts in their subset of arthropods. Usually accumulates a state photo record for each species but doesn't accumulate records more generally.
All living things:
http://www.inaturalist.org/ - This site is a good resource for crowd-sourced IDs, tracking personal life lists and sightings, and it accumulates sightings. It has a basic phone app for snapping a picture and submitting a sighting from it. Sightings are classified taxonomically and regionally, making it easy to search for taxa at any level from a county, state, or county (e.g., skippers in Maryland or subfamiliy Noctuinae in Calvert County). Your sightings don't have to have a photo, and you can submit audio observations. You can import photos in bulk from your computer or online photo services like Flickr or Picasa, and location, date, and ID info can be automatically gleaned from photo tags.
http://www.projectnoah.org/ - This site can provide crowd-source IDs and it accumulates sightings. The sightings are only very simplistically classified and not in much of a taxonomic tree, so while you can search for all insects in North America, you can't search for all beetles in Maryland or all skippers in Howard County. After trying out this site, I found iNaturalist much more useful.
Both of these two sites allow users to add their sightings to focused "projects" (called "missions" in Project Noah) or to start their own. Sightings can then be downloaded in bulk for a project.