OpenTable is definitely one I would recommend.  I think having your menu up as a jpeg image or using this app:   http://www.facebook.com/menutab  would be good (I haven’t tried this app so I don’t know how well it works)

If your restaurant does coupons or deals you could use Facebook deals or a coupon app (many out there) but not all restaurants do discounts.  

I also always recommend having people try to get their fans onto their e-mail list  I like this app that the Melting Pot has:  http://www.facebook.com/themeltingpotoflittleton/app_102282819826505  Combines the Like-gate with the reservations and e-mail list and a poll all in one app.  I think they may have had this custom built.  

Hope that helps!