6th Floor Museum really is excellent and they've done a great job of using the new iPod guides that have become popular.
I'd also like to chime in say the museum is GREAT. Not an exaggeration - I've been to my share of museums in the US and abroad... And the 6th floor museum in Dallas is my favorite of ALL of them (probably becase I'm not a huge art fan, and this museum tells a great story). For those that don't know, it's on the 6th floor of the Texas Schoolbook Repository, where Oswald fired the shots. They still have the corner set up as it was in '63. You can look through the window and see the little "X" on the street marking JFK's position... It's cool, if not a bit creepy.