This is my list. My assumptions are: a regular map (not something like Nipperhouse or port where some races gain exponential strength), max level, full items and a player is of exceptional quality (I.E. someone who can use the race to the best of its abilities).

33. Rapscallion
32. Hell-hunter
31. Warden
30. Panorama^1
29. Chameleon
28. Magician^2
27. Dragonfly
26. Orc
25. Eye Ra
24. Shadow of the Void
23. Genocide^3
22. Flame Predator
21. Beast
20. Bloodmage^4
19. Undead Scourge
18. Night Elf
17. Raiden
16. Die Xonvert
15. Crypt Lord^5
14. Archmage Proudmore
13. Succubus Hunter^6
12. Strider
11. Athena
10. Hells Demon
9. Shadow Hunter
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I think there's a HUGE gap between all of the previous races and the following 8 (or the BIG 8). With truly skillful players, any of these can be nigh unplayable.
8. Vagalion
7. Santa
6. Jack
5. Nebula^7
4. Molecule
3. Spiderman
2. Human
1. Vagabond

^1 - this race can increase in value a lot for the TEAMPLAY if you have someone who has a high skill ceiling and is selfless (doesn't care about stats), so the potential for this race in a 10 v 10 for me would be significantly different than just overall strength of the race in most situations.
^2 - Magician is an interesting case as it can potential be up at Big 8 (invisible bird with 150 health), but the randomness and overall situation leaves this race quite low.
^3 - same as ^1 (panorama)
^4 - Bloodmage's value significantly increases in large team situations (10 v 10) and a large amount of bloodmages can overpower nearly anything by raw force (we've done such an experiment).
^5 - Somewhat same situation as Athena ---> this race is incredibly powerful in the winning team, but significantly worse in the losing situations. Both of these races can possibly be even in top 5 as far as devastation goes, but it's not consistent, thus the low place.
^6 - A full powered up succubus hunter can be nearly unkilleable, but considering the effort needed to get it powered up starting the first round it suffers from a relatively low placement.
^7 - Nebula, IMO, can possibly as the single MOST USEFUL race in WCS in the right team environments: it is incredibly strong in dueling (1v1) and swarming scenarios (1v5+), but it also gives one of the best tools for the team to succeed, so I'd possibly rate it as the strongest 10v10 race out there.

As noted above, these assessments were done in case of the nearly perfect player example. If I'd have to say the race strength on average, I'd pick human, spiderman and molecule as three strongest races probably followed by hells demon and then Athena or Crypt Lord. Race strength also varies drastically with maps, players and teams, so it is incredibly difficult to pin it down.