This superb Array formula deserves all the merits from J-Walk.
Found on Dick Kusleika's site (http://www.dicks-blog.com/)

***
Despite the step-by step description I do not manage to get the formula
to work!
***

Here it is:
This formula isn't very long, and it's really not all that ugly.
But it's one of my favorite formulas:


=IF(MONTH(DATE(YEAR(NOW()),MONTH(NOW()),1))-
MONTH(DATE(YEAR(NOW()),MONTH(NOW()),1)-
(WEEKDAY(DATE(YEAR(NOW()),MONTH(NOW()),1))-1)+
{0;1;2;3;4;5}*7+{1,2,3,4,5,6,7}-1),"",DATE(YEAR(NOW()),
MONTH(NOW()),1)-(WEEKDAY(DATE(YEAR(NOW()),
MONTH(NOW()),1))-1)+{0;1;2;3;4;5}*7+{1,2,3,4,5,6,7}-1)


To use it:

1. Copy the formula text to the clipboard
2. Activate a sheet and select a 7-col by 6-row range
3. Press F2
4. Press Ctrl+V to paste the formula into the active cell
5. Press Ctrl+Shift+Enter (to make it a multicell array formula)
6. Format the cells using the "d" number format.

Voila! You have a calendar for the current month.