Lots of food. Weddings can be a long day, guests may have missed a meal if you wedding is near lunch and for those who don't know anyone its nice to have some food to occupy yourself with.
Decent non-alcoholic drinks when people turn up at the reception (2 weddings now I've been to where drinkers got chilled fizz or Pimms with lots of fruit and I got room temp concentrated OJ. Bleurgh. What's wrong with a nice cold elderflower or something?).
If you're having children then make sure they're really well catered for - entertainment, food, somewhere quiet to go if they get overwhelmed. It makes it more fun for them, their parents and all the other guests.
Do try and get round to talk to each of your guests, even if you split up so bride talks to 'her' guests and groom to 'his' - good to do between courses if at no other time. Makes everyone feel included and warm and fuzzy.
A tip for you - try and take a moment after the ceremony where it's just you and your groom - it's so special to just have those few minutes to soak it all in and enjoy being married before the day takes over again.
I went to a wedding recently where all guests got an email with an itinerary of when food would be available, when dancing would start etc etc - as a guest battling pregnancy sickness it was so helpful to know when I could expect to be given food and when it might be worth having a handy cereal bar.
Try not to have a massive long walk between any two places (parking and venue is the obvious one) as some guests may only wear heels for events like this and will be quietly cursing you for their blisters! ;)
Make any 'quirky' activities optional. Not everyone is comfortable putting on a silly hat and feather boa for a polaroid. My dad would probably walk off in a massive grump if he was forced into this sort of thing!
And try to have fun and enjoy it. It's over before you know it. And the day is less important than the marriage.