BreastFeeding
When it comes to your baby's health, there is no better way to protect him from illness other than breastfeeding.  This should be a priority.  Not only will you aid in your baby's development but you will also save money... a Lot of money. 

A little math:  $40.00 per week * 52 weeks per year = $2080
And that's a low estimate.

Sometimes, however, it is not possible to breastfeed.  The Hippa act requires companies to give new mothers 6 weeks paid leave from work to care for there child but it is recommended that you breastfeed as long as possible.  I was able to breastfeed for eight before I "dried up" and I didn't have to work.  You can use a breast pump to prolong the drying up process but it will happen eventually and then you will be forced to go to formula. 

When using the breastpump it is a good idea to store your breastmilk in the freezer.  Breastmilk is good for 1 year after it leaves your body if it is frozen.

Here are some good deals on breast pumps.