Today is a flexible list of your Events and Tasks for the current day with several preferences you can set to modify its behavior. You can set it to be visible all the time and float on top of all open window. Clicking on the Event in Today opens it up in iCal so you can see the full details. This works best with a larger screen where you can drag Today off to the side to keep it out of the way. You can also set Today to show tomorrow's Events as well. You can create new Events and Tasks directly from Today without opening iCal and you can set keyboard shortcuts for showing Today and creating Events and Tasks. Because Today only shows Events from the current day (and optionally tomorrow), it is best for people who have many Events to keep track of each day.
Today costs $22US and is available here.
MenuCalendarClock costs $20US and is available here.
Dashboard Widget. It presents a scrolling list of upcoming Events (no Tasks, but there are plenty of other Dashboard Widgets for Tasks). As with the others, clicking the Event name opens the Event in iCal. You cannot create new Events from the Widget or set shortcut keys. Even with these limitations, iCal Events is my personal favorite because it has an attractive, easy to read presentation and can be viewed with a quick tap of the F4 key (to activate the Dashboard). It is best for people who have a medium number of Events per day and month. Plus, it is free.
iCal Events is free and can be found here.