Wow, Fotze actually has some good advice!
My boy will be 3 in May, and although there are a ton of bad days, the good ones make you forget them in a hurry.
Just have to agree with a few things already posted.
1) Don't cheap out on the crib, car seat, or stroller. These are, IMO, the main places where your child's safety is somewhat out of your hands. Don't go crazy, but don't go Wal-Mart.
2) Go buy a Diaper Genie 2. Somewhere around the 3 month range, poo starts to smell and garbage bags are no match.
3) Always remember that you and your wife (or baby mama) need your alone time. The baby can safely and comfortably sleep on it's own after 3 months or so. Even if your time off is only 3 or 4 hours a day, make a point of cherishing it or you will go crazy.
The last piece of advice is to never, ever underestimate what your child is capable of. They learn things at an astonishing rate and have incredible memories. Don't be the jerk Dad that pushes your kids too hard, but don't be the guy that holds them back either.
Oh, and put anything you care about into storage because it will get wrecked. No, seriously.