restaurants between L.A. and Palm Desert
Where in LA are you coming from? After a little fun with Google Maps, I've found that the halfway point from the far Westside is roughly in Bloomington/Colton ... there are lots of good taquerias there, and a decent Thai place or two, but otherwise I can't help you much.
If you're coming from downtown LA, halfway is almost exactly in downtown Redlands, where there are some better options. I'd recommend Farm Artisan, Eureka!, or Dhat Island Caribbean Creole. If it's a pleasant evening and you want to relax outdoors before dinner with some fine beers while watching the occasional small plane landing, I can highly endorse Hangar 24 Brewery (no kitchen, but food trucks a couple nights a week).
On edit: if you can persuade your friends to come as far west as Claremont, I'm happy to report that, after a few opening-months miscues, Union on Yale really seems to finally be hitting its stride.
I trust (or at least hope fervently) that the recommendations of Denny's and Olive Garden are an attempt at ironic humor? In any case I suggest one of the far flung outposts of El Tepeyac for this meet up. http://www.yelp.com/biz/el-tepeyac-restaurant-redlands and you can even get a discount coupon if you would like: http://www.restaurant.com/el-tepeyac-mexican-food-redlands-mexicansouthwestern-restaurant-pid=41742
If you are looking for something more akin to "fine dining" than El Tepeyac offers then I've heard that this place does a credible job (but have not been) http://www.farmartisanfoods.com/