As someone who has a regular schedule of weekly meetings and appointments—work meetings, after-school sports for my kids, and so on—it’s always helpful when someone who wants to schedule a meeting with me mentions the day along with the proposed date and time. For example, when I’m asked if I’m available on May 6 at 3 p.m., I have to look at my calendar; but if I know that May 6 is a Tuesday, I can immediately reply that I can’t do meetings after 3 p.m.

Day-O’s calendar display

Which brings me to my biggest gripe about OS X’s Date & Time menu-bar display (enabled in the Date & Time pane of System Preferences): It shows you only the current date and time. There’s no option to display, say, a monthly calendar when you click in the menu bar. Sometimes I’m on the phone or writing an email to set up a meeting, and I’d like to know what day of the week a proposed date falls on—since I’m no calendar savant, I need to look it up.

Full article here:
Day-O review: Me say day on the Mac’s menu bar (Macworld)

What we like about this little program is that you can customize the date display exactly to your liking. For example, if you want to see everything at a glance with no abbreviations, you could use the Date & Time format string EEEE, MMMM d, y h:mm:ss a z which produces this:
Unfortunately, it won’t flash red or sound a warning that it’s April Fools Day, and that your friends or co-workers might try to prank you!