As you'll notice, I've moved your post to the Backcountry Beginners section where there is quite a bit of information. The first (sticky) post in this section, by phat, has excellent information. You may want to read some of the other fairly recent posts, too.

Have you checked out the articles on the home page of this site, left hand column? There is lots of information there on gear selection including some excellent gear lists.

For packs, the most important issues are fit, fit and fit. The pack must fit your body, it must fit your gear, and it must be comfortable for you with your gear inside. That's why it's highly recommended to acquire the rest of your gear first and the pack last. The best thing is to box up the rest of your gear, including the equivalent in weight/bulk of a week's food and water and take it to the store when shopping for packs. If possible, make an appointment first. (This will also let you measure the total volume = length x width x height in inches. 1 liter is approximately 60 cubic inches.) If that doesn't work, at least have all the gear ready as soon as you get the pack home. Before you take the tags off, load it up with the stuff and carry it around the house for a couple of hours. Boring, but that will let you know if the pack is a keeper while it's still clean and returnable. With two of you and two packs, that might be the better solution.

If you're not sure you're going to like backpacking, then borrowing or renting gear or buying second-hand is a good way to start. It's more important that the packs fit comfortably, though, or you'll be miserable.