This is possibly the first thing that you'll have to line up. In most cities popular wedding venues are booked a year or more, even years, in advance. Find out what the venue will provide: do they offer catering, or do you need to make separate arrangements for food? Will their staff set up the room for you? Is there a deejay on staff? What's the parking situation? Will you be having the ceremony and the reception in the same location? The more popular places will anticipate your questions and help you with planning. Other locations may not be as helpful, but more affordable.
A professional is the way to go, preferably someone who has done a few weddings. Not only are there posed pictures, but there are many opportunities for candid shots during the processional, recessional and the reception. A good photographer will be virtually invisible. I've seen a few blocking guests' view during the ceremony; a no-no as far as I'm concerned. A good photographer won't need every member of the wedding party to stop and pose during the processional - but everyone should smile - that's hard to edit in afterwards! Sit down with your photographer and discuss exactly what pictures you want taken. Experienced professionals will have suggestions for you, but let them know if there is anything out of the ordinary that you want.
There are some great caterers and bakers in town. If your venue doesn't provide food, shop around, ask for suggested menus. Surprisingly, several of the grocery stores in town have excellent bakeries and cake decorators who do an excellent job with wedding cakes.
Many deejays double as the master-of-ceremonies during the reception. Work with your deejay on a schedule for your reception, pick out the songs together (although a good deejay will know what kind of songs work best for different parts of the ceremony) and make sure she has a list of all the relevant names. Some deejays will provide a microphone for your officiant and any musical accompaniment. Check with your musicians and your minister for their needs. For example, since I don't memorize my weddings (each one is different) and read from a script, it is awkward for me to juggle a hand-held microphone and ask for one on a stand, or at least a clip-on.
You're probably going to be somewhat nervous and under some stress on the day of the wedding. Hiring a wedding coordinator will take the pressure off. A wedding planner or coordinator not only does a lot of the leg work in lining up your vendors, but also helps "direct traffic", i.e. get everybody lined up and in place on time for the ceremony. A coordinator will also handle any last minute problems like missing flowers, late arrivals or issues with the sound system so that you can relax and enjoy your big day.
There are numerous other details and many other team members that will contribute to making the day go smooth: florists, bridal and tux shops, printers (for invitations) and of course, don't forget, an experienced officiant!