Awhile back I bought a laser level to help with LOS for Dust Tactics.  I also have found it very useful in Dust Warfare.  Since obstructing terrain isn't done by true line of sight, but is done by drawing lines across the board between bases, the laser level comes in extremely handy to quickly check if there is any terrain between your unit and the opponent's.

Here's the laser level I have - Amazon lists it as $20, but I think I got it for around $15 at Home Depot.  It's about the size of a computer mouse, and can draw a line across the battlefield.

http://www.amazon.com/Johnson-Level-Tool-9250-Laser/dp/B001C3C0HK

You can also use it to provide lighting effects when your laser grenadiers shoot up a BBQ Squad! :-)

Hmm, just read a customer review and apparently the one you get isn't the same one pictured (the one pictured is the one I have and it works great), so I thought I'd provide a link to it on a different website too in case that's helpful.

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10053&langId=-1&locStoreNum=6175&productId=202911563&storeId=10051#BVRRWidgetID

as much as i do not want to list competitor items here, warhammer has a laser i think for 12 bucks is meant for this sort of thing (also prices very per store)

http://www.games-workshop.com/gws/catalog/productDetail.jsp?prodId=prod1410001

The GW one is a bit different.  It's more like a laser pointer, which would be helpful for determining true line of sight.

The one I have doesn't project a point, but draws a straight line across the table, which is good in DW for determining which units are obstructed.

Both could be useful in their own ways.

 Yeah, the GW one also that makes the "point" a "target reticle and gets quite large after about 3 feet.  Not nearly as useful.