Hi Todd!
You can enjoy breakfast, lunch or dinner at any of the restaurants that accept the dining plan. Here is a link to the dining plan brochure that lists them all:
http://adisneyworld.disney.go.com/media/wdw/images2003/languagespecific/eng/nontheme/tickets/2009Dining.pdf
There are a handful of choices for dinner at both Magic Kingdom and Animal Kingdom. At the MK, dinner is served at Liberty Tree Tavern, Cinderella's Royal Table, Tony's Town Square, The Plaza Restaurant and The Crystal Palace. At the AK, you can have a sit down dinner at The Tusker House and Yak & Yeti. (The Rainforest Cafe also serves dinner, but is not included on the dining plan.)
Reservations are strongly recommended, especially during the free dining promotion. I would suggest calling exactly 90 days from the first day of your vacation for the best chance at securing the meals you want. There is no additional charge for character meals. If they are on the plan, it will only cost you your dining credit. The only exceptions are Cinderella's Royal Table at the Magic Kingdom and Mickey's backyard BBQ at Fort Wilderness. These are included on the plan, but require that each person redeem two table service credits.
I hope this helps! Have fun planning your vacation!!