Have you ever tried to search for something specific to R, such as a command or tutorial? Its torture. "R" isn't a long enough search string to be specific so the results are pretty random. This is a collection of sites that will help you find answers.
R Statistical Language - This is a multi-site search tool that includes several universities, popular forums and the official R sites. This usually returns quality results on the first try.
RSeek - Another R specific search engine that usually returns good results on the first attempt.
R Mailing List Archive - For error messages and program debugging, this site simply cannot be beat. If your code is breaking, there's a good chance that someone has asked the mailing list about it before.
rstats - If you've checked each of these resources & you're still having trouble finding what you need, try searching your favorite search engine and include rstats in your search string. This will also be helpful for searching Twitter.
Honorable mentions go to Stack Overflow & Cross Validated. These sites are great for getting answers to specific questions, and have tags specific to R. Heads up though, this is not the place for generic or open-ended questions.