Bob asked if I knew of an online timeline tracking a child's development. Here's one. Note that I prefer using the references in a couple of books. The What to expect... series ("when you're expecting", "the first year", "the toddler years"), and better IMO, Caring for your baby and young child. Birth to age 5 from the American Academy of Pediatrics.
The books explain that developmental milestones vary a great deal so I wouldn't necessarily rank my child against one of these timelines. In fact, at one point I became an enemy of them as it's very easy to become a little paranoid if they describe something you haven't seen happen yet, or irrationally proud when you think your child achieved something long before (s)he's suppossed to. Then again, the same thing happens as you inevitably compare with other babies that are about the same age as yours.