My new favorite workout for intensity and volume is the "actual pyramid" which is more of a triangle, and "actual" because the point is at the top. Start with one rep and add a rep each set until failure. Try to do another set. This is intense because of course each set is more difficult than the last.
For Russian Push-Ups:
1. 1
2. 1 1
3. 1 1 1
4. 1 1 1 1
5. 1 1 1 1 1
6. 1 1 1 1 1 1
7. 1 1 1 1 1 1 1
8. 1 1 1 1 1 1 1 1
9. 1 1 1 1 1 1 1 1 1
10. 1 1 1 1 1 1 1 1 1 1
11. 1 1 1 1 1 1 1 1 1 1 1
12. 1 1 1 1 1 1 1 1 1 1 1 1
13. 1 1 1 1 1 1 1 1 1 1 1 1 1
14. 1 1 1 1 1 1 1 1 1 1 1 1 1 1
15. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
16. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
17. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
18. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
19. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
20. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
21. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
See, more of a right triangle.