I don't bother with a diary. I just use a wall calendar. Consequently I need a decent amount of space under each day so I can write in perhaps 3 or 4 appointments per day. For most wall calendars there is room to squeeze in one thing like "Dentist 4pm" and that's it! I've googled 'large wall calendars' to no avail.
What's your current wall calendar like - is it any good and where did you get it?