There are a couple of options for you.
1. If they are going to be spending time at WDW, you can buy them Disney Dollars. Disney Dollars work the same as cash, but are good in WDW.
2. Do a search on citysearch.com. You will be able to find most of the restaurants in the Orlando area, including WDW and Unicersal. Call them up and you should be able to purchase gift certificates over the phone or off of a website.
3. Go to you local Outback (Outback Steakhouse, Bonefish Grill, Carraba's, Roy's etc), Darden (Red Lobster, Bahama Breeze, Olive Garden, Smokey Bones etc), Bennigan's, or whatever chain Restaurant. Buy gift cards from them, they are usually good at and Company wide location. For example, if you buy a gift card at Outback Steakhouse, you can use it at Bonefish Grill, Roy's or any of the Outback operated restaurants. If you go to outback.com, and go to coorporate info, it will list all of the other companies they own with links.
4. Go to each Company's website, you can purchase gift cards on line for anything, Wolfgang Pucks, Rainforest Cafe, Emeril's etc. Just do a search to find the company site.
Keep in mind that Central Florida is a HUGE tourist area, most of the chain resturants may have a new concept opening in the area and the websites should have something.
Also, keep in mind that some companies may "charge" the recipient for not using the gift card. Darden Restaurants deducts $1.50 a month if the card is not used after 24 months. Be sure to ask about this when purchasing gift cards in advance.
Hope this helps!