I would start out with 3 things:
1. Research- bindings
3. Research-riding how-to's
Personal preference and different riding styles seem to have alot to do with what one rider thinks is a good board over another, so any advice you get from others should be tempered with that in mind.
The threads here are full of advice on beginners boards, in addition there is a list of boards with reviews pros and cons from folks who have demoed them under the "Gear" link.
So you might spend some time searching the forum and forum archives, as you will find all kinds of info on choosing a new board.
There used to be a board finder before the new site was put up and I see it is still under construction so maybe check back later on that one.
What you might do before you buy is seek the advice of someone at a Pro-Shop and actually ride a few first so you make a good purchase decision without wasting money.
If you have some friends that ride you might try to hit them up for a demo ride or two (don't forget to help out with gas etc) and see if you think this sport might be for you and your girl before you put down some change and find out later its not.
Everybody's story is different but I started out with a borrowed board then bought a cheap off brand continuous rocker board that had "universal one size fits all" bindings so that more than one rider could use them.
The disadvantage of universal bindings is that they generally do not "custom fit" your foot and
therefore will probably not be as comfortable as they otherwise could be with a one size binding.
After about 6 months I bought a CWB Sol off the net.
After 3-4 years of riding I added an O'Brien Natural, Hyperlite Era, Roam, Ronix One and a few others.
The sport can be expensive when you consider gear, gas, boat, life jacket, handle/line, injuries etc and whatever you spend on a board you shouldn't skimp on bindings as they are just as important if not more so than the board choice you make.
Anyway good luck to you in your search for a first board.