I like the concept behind rituals, giving players pay-per-cast spells largely intended for out of
combat uses, but I hear that there's no shortage of groups that just don't use them (or don't like them). I don't get to play, and since I do like rituals often pepper treasures with rituals that have an immediate (or soonish) use. For example, if the adventure calls for the players to find a way into an underwater grotto in order to confront and star cult, I'm likely to put a Water Breathing ritual (or scroll if they're too low level). If they bust up a necromancer's crypt, I might put in an Undead Servitor ritual for kicks.
Oh, and I also throw in residuum or ritual components to make sure they can use it (as well as padding treasure out if they like to use them, so they don't feel like they have to "choose" between ritual usage or loot).