If pictures are important to you, you need to hire a pro. With years of experience, and plenty of backup equipment, pros are dependable and well prepared and able to anticipate once-in-a-lifetime shots that others might miss. Hire services that you can depend on. You’ll have more important things to think about on your day than whether or not the photographer is doing his job.
Expect to spend at least $1200 for a basic package, up to several thousand that might include multiple photographers or assistants and advanced digital presentations of your images.
Find a photographer whose style you like. Some take a documentary approach, staying out of the way, capturing important moments, and only stepping forward to pose you for the occasional formal. Others will take charge and stage the whole day for you, and create fairy-tale images that may or may not be what you want. Some will be in between.
As @Dorkgirl said, try to find out who will actually be showing up to shoot for you. Many studios employ a number of photographers, and thought hey usually try to match you up with someone best suited, your chemistry might not mix. But those studios will be cheaper than hiring a well known individual.
Also find out exactly what you’ll be getting. The cheapest route would be to find someone willing to sell you the files, then you can have them printed as you wish. Of course, you may end up spending more money and certainly more time getting prints and albums made on your own. You may be offered printed proofs in an album, or digital images on disk or online. Prices may or may not include final albums.
Shop around, read the fine print, and don’t be swayed by sales pitches.