I have to admit, I LOVE the Bubble Calendar.  It is a "poster sized calendar with a bubble to pop every day."  If you're looking for something cool to give your customers, you can even have them customized.  Just one customization idea:  if you're a tax attorney or CPA, imagine having one with your logo as well as April 15th (and other appropriate deadlines) highlighted in red.  I'm ordering mine today.