Things to consider purchasing before having a baby

Traveling

Car seat: Consider something that detaches from a base which is installed in the car, it'll be easier and faster to move the baby in + out (a real bonus in cold weather). A second base for a second car is cheap.
Car seat wrap (?): We used a blanket, but sometimes would have liked a cover the baby couldn't remove.
Stroller: If you get a carseat that pops out of a base, consider the Combi Flash Stroller Frame - you can just pop the carseat in and go. Once the baby grows out of the carseat, you'll need another one, but until then it's incredibly simple. If you get a separate stroller, you'll need one that lays flat for an infant. We made do with the carseat + frame until we got a Baby Jogger City model - the ease of folding and adjusting was the main selling point for that one.
Portable Crib: If possible, test the opening/closing mechanism before buying. Newer ones are much easier than old ones, which may mean avoiding hand-me-downs. Some have many added features at premium cost, if you think you'll use them, it may be worth it. We chose the simplest Pack-n-play and have been happy.
Portable crib sheets: At least two.
Diaper Folder: Whether you get an official diaper bag or not, you'll want a "folder" that you can lay the baby on when you're out and about, something that will hold 2-3 diapers and a packet of wipes. Ideally, find one that you can close with one hand. Keeping an extra loaded one in the car isn't a bad idea either.
Diaper Bag (?): Bags for babies have tons of features, but what you need may depend on your baby's lifestyle. You may want to use a bag from around the house until you reach a point where you say "I wish this bag had an insulated bottle pocket!" or some other unusual feature.

Diapering

Changing table: Look for utility first - you need to be able to hold the baby with one hand and get clean diapers, wipes, and new clothes with the other. Something that will function as a dresser once your child is older may be a good idea. Make sure it won't fall over (or can be anchored to the wall) if you're going to have an active baby.
Changing pad: Something to go on top of the table to protect/contain the baby. Look for some absorbent pad covers as well.
Diaper pail: Something that attempts to contain smells is a good idea. We have the diaper champ. You may need an additional garbage can because small pieces of trash or particularly bad diapers won't always go down the tube...

Sleeping

Crib: Adjustable mattress height and railings will make life easier. Test the operation of the railing, you'll be moving that a lot.
Mattress: Just pick the right size.
Waterproof mattress pads (3): You're not looking for comfort - just something absorbent on one side and waterproof on the other, to protect the mattress. Layer them. Keep an extra one for the porta-crib.
Crib sheets: Get at least two.
Night light: Babies aren't afraid of the dark, just get something that will let you move around the room without waking them. Consider a dimmer for the lightswitch.

Things to consider in your nursery

Rocking chair: Put a table next to it so you can keep water, a book, and late-night snacks (teddy grahams) there.
Storage: Drawers, book/toy shelves
Lighting: Task lighting for the changing area, mood lighting for 3 a.m. feedings, blackout shades for the window.
Music: For all of you. Consider a remote control.
Clock: So you know how much fun you had last night
Blanket for parents: Temperature regulation is a real trick, and if the baby's eating, you don't want to stop to find a sweater.

Things you'll probably get from friends and family without asking

Blankets
Books
Hanging toys / mobiles
Diapers + wipes
Clothing: Onesies, sleepers, outfits, funny little hats
Cold weather gear: Snowsuit, booties, hat

Feeding

Bottles: For a start, get at least two. You may want to watch news about Bisphenol A, the toxic chemical that leaches from heated bottles, and wait for one of the major manufacturers to release a bottle that doesn't use it.
Bottle warmer (?): We laughed at this little device until we needed to heat bottles regularly, and then it was awesome.
Boppy-type pillow and covers.
Lansinoh nursing pads
Burp cloths: You can get something baby-specific, or pick up some new hand towels that you'll like having around after the baby is done spitting all over everything.
Bibs: If your baby is particularly messy, a bib can mean fewer clothing changes. Get a bunch.
Pacifiers: While you may want to avoid giving a newborn a pacifier on a regular basis, it can be helpful to pick up a few Soothie newborn pacifiers. You can sterilize it, pop your finger in the backside and let the baby chew on that for a bit, which can be hugely calming inbetween meals. Plus, it's fun to have the baby chew on your finger.

Other

Bath seat (?): If you're going to bathe with the baby, you won't need this. If you going to try to wash up in the sink, it could be helpful to keep the baby contained while you operate the sponge.
Body care supplies: Bath soap, lotion, diaper cream, baby powder, nail clippers.
Monitor: You'll want to hear the baby remotely, sometimes. We like having video now, because you can tell what the baby's doing without having to go in the room, but early on sound was enough. If quiet babies make you nervous, look up the Angelcare movement monitor.

Play

Bouncy seat
Front carrier or sling: If possible, borrow one and try it out. Some are hard on your back. We had a baby bjorn, which fit fantastically, but a September baby didn't get to use it much before it was cold - and once it was warm, she was too big. Look for a used one.
Gym: It's good to have a way to hang toys over the baby while they lie on the floor. Some types attach to a boppy, some to a blanket, some are freestanding.