There's another new DVD, to be released January 27, called Spongicus.
Also, in other news, there will be 23 new episodes next year, according to this page found by SpongeBobfan1987. Depending on when Season 6 is finished, most of those are probably from the already confirmed Season 7, but this still tells us that Nick will be celebrating SpongeBob's 10th anniversary. :P
Running time is 90 minutes, so it sounds like it'll have 8 episodes like most of the recent DVDs have had. News credit goes to TVShowsOnDVD. :PBikini Bottom turns upside down when SpongeBob and Patrick become gladiators in the title episode Spongicus. Plus more fun and foolishness as Squidward tries to write a music composition, Plankton starts a rock band with Patrick, Squidward and SpongeBob, Mr. Krabs becomes more obsessed with money and SpongeBob taps into his spongy-ness all on one DVD!

Also, in other news, there will be 23 new episodes next year, according to this page found by SpongeBobfan1987. Depending on when Season 6 is finished, most of those are probably from the already confirmed Season 7, but this still tells us that Nick will be celebrating SpongeBob's 10th anniversary. :P