The best online Mandarin language training resource happens to be free, but unfortunately it isn't for beginners:

http://www.slow-chinese.com

Aside from the usual books, I'd suggest using your local library to get your hands on some Pimsleur and/or Rosetta Stone if possible until you get up to speed for more advanced resources.

You'll also want to frequently look things up in a Chinese/English dictionary, but whether it's online or in book form is up to you.