It seems you can’t walk into tool land at your local home center without multiple laser beams guiding you on a straight path to the checkout counter. Some laser products are gimmicky, while others are a true enhancement. If your old workhorse-of-a-miter saw still cuts true but your eyes are not what they used to be, retrofitting a laser guideline is a great idea. Irwin’s new miter saw laser guide sits flush against the saw blade for an accurate line. The guide has an automatic on/off switch that is activated when the saw spins at over 400 RPMs, projecting a visible red laser line just to the left of the cut. The laser guide fits all 8 ¼“, 8 ½”, 10” and 12” miter saws, with the exception of Bosch, Ridgid, and Protech. Expect to pay under $30.
There are some very good laser levels out there with models for homeowners as well as the pros. One of the best brands is Pacific Laser Systems (PLS). PLS definitely has the best beam definition and accuracy in the market.
The units start at $200 and go over $1000. For the homeowner, the reasonably priced PLS2E is a good unit and will make everything from hanging cabinets and laying out rough-in plumbing to hanging artwork and installing tile a snap. While $200 sounds like a lot, it's a good investment if you have a lot of projects that need level and plumb lines.
Here's a helpful article on picking the right laser level: http://reviews.ebay.com/Picking-the-Right-Laser-Level_W0QQugidZ10000000002179569