My suggestion would be to dine at the restaurant at the Arboretum. The food is perhaps not "LTH-worthy" but very good nonetheless, the view is spectacular, and the money you spend there will go to preserving one of the Chicago area's living treasures.
If you decide to leave the grounds for a meal, Fabulous Noodles is nearby, as is Lao Sze Chuan in Downers Grove -- both are on Ogden Avenue. Other places worth mentioning are Country House for a really good burger (they also have buffalo and ostrich burgers), Bella Pizza and Hot Dogs (a new venture from the folks at Gene & Jude's), and Yerbabuena (good food but erratic service). Country House is in the strip mall at College and Green Trails in Lisle, Bella is in the Seven Bridges complex on rt53 in Woodridge, and Yerbabuena is in downtown Lisle on Main St.
Oh, and I second the recco for Chef Paul's...if I left the Arboretum grounds, it is where I would go. Great German/Bavarian/Bohemian food with an equally great selection of beer. Note that since it became smoke-free, even in the (large) bar area, it has become a destination spot for the soccer-mom-family crowd...if there will be no children with you, dine in the bar area.