Sticky Posts feature will place the new or published post at the top of the front page without changing the timestamp. In WordPress 2.7 Sticky Posts is a built in feature which has Sticky Posts check box on the write screens and also in Quick Edit screen.
How to enable Sticky Posts in 2.7 and in prior WordPress versions here http://www.thepicky.com/blogging/how-make-a-post-sticky-in-wordpress/
