Example: M T W T F = Days of the week
Some of these are fairly familiar and others... obscure corners of science? :) Well, I have to challenge you guys! Hopefully there's a good mix of difficulty.
Feel free to post answers (or questions). Everyone should assume the comments contain spoilers.
1. R O Y G B I V
2. E G B D F
3. J F M A M J J A S O N D
4. M V E M J S U N
5. O B A F G K M
6. P R N D I L
7. K M G T P E Z Y
8. O T T F F S S E N Z
9. A B B B B B B B B C D E K
10. G B D F A
11. H H L B B C N O F N ...
12. W A J M M A J V H T P T F ...
13. D C B A F G E
14. S P D F
15. K P C O F G S
16. P R K B Q K
17. T T C P Q G
18. H S K T K T H S K T K T E E M N H S K T K T