I am creating a formal invitation letter.

Can recommend some simple and easy-to-use software for creating the invitation letter?

Microsoft Word

adobe photoshop

totally agreed with u

izzit need to print out later?..
if yes M$ words should be the most suitable s/w for u

but u have a special design with alot of graphics.. then use photoshop

sure words is the most simple one.. also have mail merge..

Its not simple to use photoshop actually - especially when comes to layout with text and the the text wont look that sharp because its considered an image. If you want to have a special design or lots of graphics, Illustrator or Corel Draw will be more than enough

well..i think when it comes to layout..Illustrator will be a better choice...at least i think it's really simple to use..but difficult to master...it's WYSIWYG...easy to drag n drop too...might wanna consider using it...

u can try to using flash if u wanna send email to everyone then u can create some animation inside also is that good hahahaha