The stock plug for the Versys is the NGK CR9EIA-9. It is an iridium plug designed for long life. It is used in lots of Kawasaki, first in the ZX-12R because it was such a bitch to change plugs. I know it is used in the ZX-10R also. It is kinda expensive.
There is another plug that works, CR9EK. It is the same reach and heat range but is a dual electrode plug first used in GSXR600. It is reported to produce a little more horsepower in most applications. It probably won't last as long. I have pulled them out of a ZX-10R at 10,000 miles and they show little wear.
I just bought a couple off ebay for $10 shipped so I will probably try them at about 10,000 miles and carry them as spares 'til then.