I agree with buy used. My must-haves for new were the crib and car seat. Things like the swing, exersaucer, toys, we got from craigslist or consignment.
Shop clearance. I did great buying my DDs clothes a year in advance shopping clearance. I got clearance prices that were better than buying consignment for her clothes. However, it helped that her size has always followed her age pretty closely, I lucked out on that.
Breastfeeding definitely saved me money, I pumped at work and I know my pump (although expensive) was cheaper than a year of formula.
Amazon Mom used to be the best deal I could find on diapers with subscribe and save, but they have since lowered the discount so it may not be anymore. A blog I follow on facebook, Baby Cheapskate, comes out with a list each week of the best diaper deals, taking into account sales and coupons.
You really don't need as much stuff as you think you might. Just because someone else has 3 swings, every activity center you can think of, and 5 playmats doesn't mean you need that many
Someone asked about convertible cribs... I didn't see too many non convertible cribs when I was looking, so we got one. We will convert it to the toddler bed, but then it will probably be passed along to the next kiddo so we may not truly convert it all the way to using it for the full size headboard and footboard.