I like to do offal Chinese-style. Not always easy to find recipes, but you can always adapt, e.g., a beef recipe, and replace the sliced beef with slices of pig liver.
Luard, The Old World Kitchen has a respectable number of traditional European offal recipes, if you prefer European-style. (I've read reviews slamming it for having "too many" offal recipes.)
Schwabe, Unmentionable Cuisine has a diverse range of recipes, from various culinary traditions.
Given the small number of offal recipes in most books, online is good. Sometimes, it helps to know what else the offal item is called. E.g., intestines: http://allrecipes.com/recipe/104414/creole-chitterlings-chitlins/
Chicken hearts are a good size to grill or BBQ on skewers. One Brazilian BBQ place in Sydney has chicken hearts as a standard item.