Nevada is a LARGE state and to see it all would require many days. Just the "small" county of Washoe (with Reno and Lake Tahoe) is over 6,600 square miles!
But, there are statewide highlights that people come to see.
1. Las Vegas, and the Strip.
2. Hoover Dam and Lake Mead
3. Lake Tahoe
4. Reno
5. Pyramid Lake (a true, prehistoric desert lake)
6. Great Basin National Park
7. Virginia City (of Ponderosa TV show fame)
8. Lehman Caves
9. Red Rock Canyon conservation area
10. Highway 50's towns and attractions along the way....
Or try this for other ideas:
http://www.nevadatourism.com/attractions.htm :-)