You might expect to get some biased advice here, seeing as I happen to be a wedding photographer. Well, that's partially true. As a photographer, I know how vital the wedding photography will be to your big day - which is unfortunately something some brides don't realize until it's too late.
No matter who you decide to use for your wedding photographer, make this the one place you don’t skimp. Planning a wedding on a budget is an enormous task, but the photography budget should be one of the last things you cut. The day after your wedding, the food will all be eaten, the cake will be gone, the flowers will be dead, and your dress will be hanging in the back of your closet, but the pictures of your day will be around forever. In the end, after it is all said and done, they will be virtually the only physical reminder you have of your day. This is the part of your wedding that your kids will see - and their kids, and their kids, and so on - so make sure that the legacy of your wedding will be something you are proud to share. The old adage you get what you pay for is never more true than when applied to wedding photography!
When it comes to actually making the decision...now that's the tough part! :) First and foremost, you should LOVE their work. It shouldn't be "good enough" or something you can just LIVE with - you should be genuinely excited about it! If you see anything in their work that doesn't mesh with your style, consider walking away. Asking a photographer to change their style to is destined to give disappointing results. How do you know if a photographer has work that you love? I always recommend visiting their blog - and visiting regularly! Their blog should have their most recent work posted on a regular basis - it will allow you to see their work across a variety of subjects and locations. On their site, the photographer can pick and choose only the best shots, so looking at the blog will offer a better glimpse of their true ability and style as it is NOW (after all, their site may be five or ten years out of date!). Also, ask to see an entire wedding from start to finish - the same files that the couple received. The photographer may be a fantastic portrait shooter, but their getting ready or ceremony pictures are less than amazing...so it's important to ensure that ALL your pictures will be what you want! Or maybe you don't really care about the getting ready pictures, but want amazing portrait pictures - so make sure they can provide that!
Almost as important as loving their work is getting along with the photographer herself (or himself)! This person is going to be with more more than almost anyone else on your wedding day - they'll be your shadow! It's important that your personalities don't clash. For instance, I'm definitely not a wallflower - I love interacting with you and your family and friends and guests. I almost always leave a wedding feeling like part of the family! If you're looking for someone to stand in the shadows and snap away ninja-style...well, it's probably not me. :)
The third thing to consider is what you want out of your photography. Most photographers can offer customized packages if their standard packages don't offer what you want, but always double check! If you want lots of prints, you might want to consider a photographer who provides you with the high-resolution images on a disc. If you want a big, beautiful album, be sure that the photographer offers that and ask to see a sample. If you're mostly concerned about viewing your pictures online, see if they will provide an online gallery.
The last thing to consider is budget - as I said above, photography is one of the few places where splurging and getting what you REALLY want is absolutely worth it! If you can sacrifice a layer of your five-layer cake, or serve pork roast instead of filet mignon, or offer house liquor instead of top shelf....well, it might just end up being a decision you'll be glad you made for the rest of your life.