Trying to get the most out of iCal.

I was inspired to ask this question when I again forgot to pay my Amazon credit card bill. I use iCal and I keep all my due dates for my bills on it, but as far as I know, it doesn't really do any good unless iCal is open and you are looking at it.

I'd like to find an addon that sets reminders or notifications for upcoming events or even just the events of that day. Perhaps this feature is built into iCal already and I just don't know how to use it.

The perfect thing would be if there is an addon out there that just puts something small on the desktop or in the menubar on days where there is an event scheduled.

Any help would be greatly appreciated. I guess the lesson to be learned here is not to use credit cards.