I tried
SmoothCalendar back when i first got my Nexus One. It was pretty, but i didnt really refer to it enough. Think it was because it didnt show enough info in the small pace - always ended up bumping into the full stock app.
Then i went to
Blik. Blik is a 4x1 horizontal or vertical widget that shows your calendar in pictorial format. For example I have physiology lecture at 2pm-4pm, and then martial arts that evening 6pm-8pm. Blik shows a picture with one word under it. So for the lecture it would be "L4" (lecture four) and the pic would be a medical snake-staff icon thingy. martial arts would be an image of a person doing a kick. The images are built in - designed to fit words in the description or name of the event. The free version only allows change each event picture individually/manually, whereas the paid version does allow for a rule to be made so its automatic, and IIRC your own icons.
Still use this widget as a quick view of my day to come or current/next appointment.
My main app is now
Calendar Pad, which has been mentioned by other users here. My widget setup at the moment is home screen has Blik at the top, screen to left of home has 4x2 week widget, screen to right of home has 4x2 day widget and then screen to left of the week widget has 4x2 month widget. Leaves enough room for other widgets and shortcuts around the edges (just!) and i have one screen 'free'.
It seems good, but im on uni holidays at the moment so havent tried it in action yet.
The app part is pretty simple looking, but has the feature of, say you're in month view - you can sweep across a week to zoom to weekview , or you can select a specific day to jump to day view. I havent seen many other calendar apps feature this way.
Links for AppBrain: