Here are the top three things I wouldn't be able to be without, now that I have a little poopy machine in the house. Forget the cool toys that you really want, like the Flip Mino, or a new Dell Mini laptop. Sure, you'll need those too, but only after you've covered these three bases.
Oxi Clean baby stain remover
This little gem is the first thing you need to go buy. Trust me. The little monster will from the beginning make huge messes, in front, back, top and bottom of anything you put on him (or her). You can buy this pretty much anywhere, this is what I bought.
A nasal aspirator
Forget that little rubber sucker bulb they give you at the hospital, you need a battery driven power sucker (the baby noses might be tiny, but they generate a good amount of goop). I got the Bébésounds Nasal Clear Battery Operated Nasal Aspirator, which has worked really well so far. Just clean it often, dried snott will clog it up. You can typically find it on Target or any other baby friendly store (be careful though, trips to these hell holes can get very expensive, specially if you bring the wife).
A non-contact infrared thermometer
This is probably the best investment I made, it's pricey, but well worth it. The ear-poking thermometers don't work on these tiny creatures. Trying to keep a thermometer in the armpit, or the little butt, is just impossible. Instead I got a Thermofocus 5-in-1 thermometer at Wallgreens. Get it, it even lets you check that bath tub temperature before throwing in the little porker.
There you have it. I hope these three little nuggets will be useful to you as well.