I just received my copy of Star Trek: Deep Space Nine Season 6 in the mail from Best Buy but there was no bonus disc. Is there supposed to be one for season 6?
Bought season 6 at Best Buy this afternoon and it does indeed have a bonus disc. The DVD contains 3 new documentaries: Inside "One Little Ship", Ferengi Rules of Acquisition: The Beginning, and Ferengi Rules of Acquisition: The Sequel.
Not sure if they'll send you the disc or not, but it can't hurt to shoot them an e-mail. DS9 Season 6 also came with a promotional offer of $20 back when you purchase seasons 6 & 7. You might want to look into that too if you didn't receive the offer.