Looking for new trip ideas

I want to complete 25 states before turning 25! So far I've been in 18 states:

1. Arkansas
2. Oklahoma
3. Texas
4. Missouri
5. Mississippi
6. Georgia
7. Florida
8. Tennessee
9. Illinois
10. Kansas
11. Colorado
12. Utah
13. New Mexico
14. Arizona
15. California
16. Idaho
17. Montana
18. Wyoming

I want to plan a road trip where I can visit 7 states, I do love both nature and cities so if the states have national parks even better! Any recommendations? I would ideally do it around May or June :)