Iíve had really good luck with Hepworth Becker guards and Black Dog Cycle Works skid plates. Iíve crashed on the trail a few times, and once on the highway (with Bark Busters) and so far zero damage to anything beyond mild scratches.
The BDCW skid plates are amazing. Theyíve taken some big hits.
Both the BCDW and Hepco Becker stuff is very carefully mounted to spread impact loads so you wonít crack your engine case on impact. Last year I saw a video where a guy actually cracked his engine. Mounting is important.