This site is a great resource for information regarding the general care, maintenance and repair of your stringed instrument. Lots of informative and amusing articles including tutorials on string types, restringing, tonewoods, and instrument restoration.
This Taylor Guitars video demonstrates the sonic differences between the most common tonewoods used in guitar building today.
Here’s a site that allows you to find out when your guitar was manufactured. Some of the more popular brands are represented here.