Your campaigns don't seem to last through all 20 levels, so I wouldn't recommend one of those unless you have reason to believe that will change.
For my money, I'd say run Red Hand of Doom. Very cool. Soft cover and least expensive, and lasts only four levels, at which point you can decide to continue the campaign or not. Starts at 5th level and stops at 9th, pushing a little higher than you usually play so that the characters end up being on the tougher side of what you've experienced and can be remembered as creme de la creme if you retire them after the campaign.
If you want to start at 1st level, then I'd say run Shattered Gates of Slaghtergard, or some adventures modules of your choice (Goodman Games, Dungeon Mag, or the first two 3.0 adventure path modules).
Expedition to Castle Ravenloft also covers only 4 or so levels, starting at 6. It's more expensive than Red Hand, but I think you'd also find it entertaining, so long as your group doesn't mind undead.
Ptolus would be a good choice too for something that will be as open ended as you want.
