I'm a green card holder, planning to apply for U.S. citizenship. I hear that I will need to supply a photo and fingerprints. Where is the best place to get these things done, and how much will they cost?
The answer to your question depends on whether you live in the U.S. or in another country.
If you live in the U.S., you do not need to obtain photos or fingerprints on your own. Unlike in past years, when you pay your $85 biometrics fee as part of your naturalization application, you are covering the cost of having your photographs and fingerprints taken. USCIS will schedule you for a separate biometrics appointment, usually some weeks after you submit your N-400.
If you live overseas, however, you will indeed need to supply photographs along with your citizenship application. These must be "passport style" and meet certain other criteria described in the instructions to Form N-400 provided by U.S. Citizenship and Immigration Services (USCIS). Also see the "Photo Requirements" page of the U.S. State Department's website for help.
In theory, you could prepare these on your own, but it's much easier to go to a professional to have them done. Ask your friends about reputable photo shops, copy shops, chain drugstores, and similar service providers that have experience in preparing photos in "U.S. passport style."
For more information about the citizenship application process, see Nolo's articles on U.S. citizenship, or consult the book, Becoming a U.S. Citizen: A Guide to the Law, Exam, and Interview," by Ilona Bray (Nolo).