I use three sources to identify birds.
1. iPhone iBird app
2. Birds of North America Field Guide
3. Fellow birders!
The iBird iPhone app is great because you can easily use it in the garden to identify birds. Right now it has 828 birds in the Western edition. The search feature makes it easy to identify birds by 15 different main variables. It includes illustrations, photographs, interesting facts, range and bird calls. It also has links to Birdpedia. It’s a lot of fun to use and there is a version for you Android users too. You can check out the iBird website for more information.
As great as the iBird is, I sometimes turn to an actual book and I use Golden Books, A guide to field identification, Birds of North America. It has a lot of illustrations and is a good general field guide for birds.
For those times when I can’t figure out the identity, fellow birders have been very helpful. Of course it helps if I can send them a picture.
As an example, this fall I photographed a mystery bird in the Goleta Slough. The BirdCam had also taken a picture of the same bird at the birdbath. Even with its distinctive patterns I couldn’t find it in the iBird or Field Guide. So I sent the picture to several friends and my friend Jan showed to a friend of hers who identified it as a Nutmeg Mannikin. Turns out it's a Southeast Asian bird that was introduced to Hawaii in the mid-1800's. You can't bird watch in Hawaii without encountering them. Enough of them have escaped from captivity in Los Angeles to form a wild population in the last decade or so. So if you’re still not sure, ask a friend!