Take a look at mine, they are all free and sound very good. I created a thunder track for controllers that I used last year. If you need somethin more professional, the ones listed above are good choices! I have folders created to give you an idea of whats inside. All are Halloween sound effect and ambiant sounds. Check out the folder Thunder Tracks for Controllers folder to start.
Adam from Poison Props has some really nice stuff. I bought one of his CDs and plan on using it in my haunt this year.
Also, Melty's page has TONS of free sounds you can download. .