When writing a business letter and because of not knowing how long printing will take, we can't put on an exact date, we can only put the month and year. Is there a comma between the month and year(ex. March, 2008 or is it just March 2008)?
There is no absolute rule. Some people use a comma, some don't. Use what your company prefers.
In the case of a letter, the date is usually the date on which it was written, not necessarily the date on which it is printed/sent.
If the information is on a flyer to multiple recipients, month and year is probably perfectly acceptable.