Oh dear! Me and diaries/calendars...
I have my PC calendar, a Palm calendar (pocket-sized and very useful for when out and about making appointments), wall calendar (this year by Brush Dance), and We'Moon (the most witchy being that it has the most detail with regard to Sun, Moon and planetary cycles, and one which I use for reference).
I used to have a Franklin Covey time management organiser which, while I worked I faithfully took everywhere, though as it was rather clumpy (approx. A5 sized) was sometimes a pain to carry around. I have also used mini-sized Filofaxes in the past.
As far as wall calendars go I have always tried to choose something alternative to the kittens and ponies type found in many retailers, and still have old Tolkien calendars along with other fantasy and myth ones. The one and only true witchy calendar I ever bought was Llwellyn's calendar from 1999, which I still have and which, being just the 2nd year they ran it, was still relatively un-fluffy, though I wouldn't touch the recent incarnations with a barge-pole now (BTVS Willow's birthday indeed!!!).
My problem has always been that I have found it hard to find just one calendar/date book that serves all purposes - small enough to be carried around in a handbag, detailed enough to include Sun and Moon cycles and significant pagan dates (without having to refer to other calendars/datebooks to do so) along with regular mundane appointments, and yet visible enough to see what you're doing for the week/month at a glance.
Yes, me and calendars/datebooks... oh dear, oh dear...