Tool - Self leveling Laser
DeWalt DW087K LaserChalkLine Self-Leveling Line Laser (Horizontal & Vertical)
Available for about $155.
http://www.amazon.com/gp/product/B000BK32EA/ref=ox_ya_os_product
For outside use it is also worth getting some red glasses
http://www.amazon.com/DEWALT-DW0714-Laser-Enhancement-Glasses/dp/B00093DJ4M/ref=pd_bxgy_hi_img_b