Calendar Pad (with Froyo support) is a very useful calendar replacement for your Android device. While it uses the database of your stock Android calendar / your Google account, the UI is nearly completely different.
With this app, you can watch all your appointments in a month, week or day just like you would do on Google calendar in your PC browser. So even in Moth view, you can see and read all your appointments at a glance. This works best in landscape mode of course.
You can set the font size for month/week/day view independently and even configure it to be different for your various Calendar Pad widgets that come with this app. The colors of your different Google calendars will be represented in Calendar Pad as well, so organizing is made very easy with this app.
You can add or change an appointment straight from Calendar Pad. Calendar Pad uses the stock Android calendar input interface for that, so no changes and full functionality there.
There is a Pro version available which allows you to even change colors and even more calendar settings etc..
NOTE: There is an edit issue on the HTC Desire. When you edit a full day appointment, the appointment date will be set one day further. You can easily correct this but you have to know about it. The developer says he is working on it, so a fix will be available soon.
I had some update issues with the widgets, too, because as most of the other calendar widgets, they may need some time after you changed an appointment. For that reason I use the stock android day widget and calendar pad for calendar use. I found this to be the perfect match on my HTC Desire.