1989 Batmobile with working shields and remote. No shopping carts or car doors hitting my car. I wouldn't have to worry about where I parked when I could just call for it to show up.
Hypo for people I know that have to take injections. Could be TOS or TNG/DS9/Voy or even ENT.
TARDIS even if it didn't travel in time. I would just love to have it be bigger on the inside.
Sonic Screwdriver would come in handy too. Especially when someone is being annoying on a cell phone.
K-9 with working side monitor that can pick up satellite signals and the internet too. Ya we never saw that on the show, but it should have been an option. K-9 would be better than R2-D2 and I'm a Star Wars fan too. He's smaller and I can understand him.
Replicator! Then I could use it to make replicas of the other props and who knows, some day make working replicas.
Oh and DRDs that could work on my car. I could use the replicator to make new parts and they could install them. Not to mention they could keep the replicator working for me. Oh and one of them would have to look like and behave like 1812.
My Top Ten: (in no particular order, cuz I want 'em all)
1. Lightsaber
2. Greatest American Hero Suit
3. Time Machine
4. Sentry Blasters (from "The Black Hole")
5. Web Shooters
6. Holodeck
7. Green Lantern Ring
8. Captain America Super Soldier Serum
9. Invisibility Cloak (Harry Potter)
10. Thor's Hammer (so I could possess the power of Thor)