The episode list of Sonic Underground, there are 40 episodes in total. Titles obtained from TV.Com. Order of shows given by Lightning_Duchess. The order is how it was in France/England (though Lightning claims this is how it was in America too).
1. Wedding Bell Blues
2. To Catch A Queen
3. Mobodoon
4. The Price of Freedom
5. Underground Masquerade
6. Tangled Webs
7. The Deepest Fear
8. Who Do You Think You Are?
9. The Last Resort
10. Come Out Wherever You Are
11. Winner Fakes All
12. A Hedgehog's Home is Her Castle
13. Artifact
14. Bug!
15. Sonic Tonic
16. Friend or Foe
17. Head Games
18. When in Rome
19. The Jewel in the Crown
20. Three Hedgehogs and A Baby
21. Dunesday
22. Mummy Dearest
23. The Hedgehog in the Iron Mask
24. Six is A Crowd
25. Flying Fortress
26. No Hedgehog is an Island
27. New Echidna in Town
28. Beginnings (Origins Part 1)
29. Getting To Know You (Origins Part 2)
30. Harmony or Something (Origins Part 3)
31. Country Crisis
32. Haircraft in Space
33. Healer
34. Sonia's Choice
35. The Big Melt
36. Sleepers
37. Bartleby The Prisoner
38. The Art of Destruction
39. The Pendant
40. Virtual Danger