I use http://doodle.com/ http://doodle.com/ for appointments (as well as it's original purpose of polling a group for the best time for an event). For appointme

I use http://doodle.com/ http://doodle.com/ for appointments (as well as it's original purpose of polling a group for the best time for an event). For appointment slots, set the options: "Participant can only choose one option" and "Limit the number of participants per option" to one. No one ever needs to log in to anything unless they want to (for setup or responses). It also has fancy options for linking with calendars, but I've never used those.