Death Valley is an amazing place but do your research first as it is in the middle of nowhere, nothing is close (even inside the park), and half the size of Vancouver Island. So A LOT of driving needs to be done to see anything.
2.5 hours from Vegas
7 hours from Phoenix
If you like hiking, Red Rock NCA is about 30 minutes north of Vegas, an amazing spot. Or 2.5 hours from Vegas is Zion NP, a truly amazing place.
Grand Canyon NP is 5 hours from Vegas or 4 hours from Phoenix. While I think the GC is also amazing, to really enjoy it you have to have time to get deep inside the canyon to really see its beauty. Unless you have lots of time, Zion is a better place to see things. If you need any tips for trails to hike, let me know. I've been to them a few times.