Wizards has lots of free mini-adventures on their website. You might try there.
Last week, I ran a one-shot adventure. The adventurers heard a rumor that W.R.A.I.T.H. was building an uber-weapon on Galapagos Island. They managed to stake out the local lumber yard and follow the wagons back to the secret base and then foiled the evildoers.
W.R.A.I.T.H. = World Reach Association for International Terrorists and Hoodlums. Think S.P.E.C.T.R.E. from James Bond.
uber-weapon - in this case, it was a giant 1000-foot long trebuchet, magicked up so it could fire anywhere in the world.
In the past, they've also used a 200-foot long wand of fireballs with a teleport system that sent the fireball bead anywhere. The Fireball itself did 1000 d6 in its target hex, 999 d6 one-foot away, 998 d6 two-feet way, etc, out to 1000 feet (rolled once, remove the highest die each foot away from target spot)
They've also used a volcano in Iceland to create a giant ash cloud over Europe and blot out the sun (remember when that really happened last year?). That adventure took a wild left turn when the party decided to fight the beholders sent to control Paris, instead of following the ash cloud back to its origins like I had planned for them to do.
What level is the party involved?