We are 5 young adults with 3 days in Queenstown, want to see Milford Sound and experience as much of the South Island as possible. What are the must do attractions? What tour company would you recommend for a heli flight to Milford etc? What would you combine with the Milford flight?

Don't know about tour companies. You will find plenty to do in Queenstown. Lots of pubs and clubs, Bungy, Jet boat, just go silly.

Heres some stuff.
Wanaka- a relaxing place in Central Otago

Arrowtown- an old Central Otago Goldfields town with an old Chinese village, 20 minutes from Queenstown

Queenstown- for adventure activities and party atmosphere

Pipeline Bungy Jump in Queenstown

Drive from Queenstown to Glenorchy- have a beer at the Glenorchy pub, after stopping and taking plenty of photos whilst on the drive

Queenstown- wineries

5 day trek of Routeburn/Greenstone Track

Walk Milford Track- one of the Worlds best

Milford Sound and Fiordland National Park- lower West Coast, South Island

Doubtful Sound in the Fiordland National Park- swim with dolphins

Top things to do in New Zealand
http://www.newzealandatoz.com/index.php?pageid=227

I'd suggest Kawauru Jet Boats - the yellow boats in the Queenstown bay, Lake Wakatipu - just there in the main part of town. Good fun!
For Milford Sound, I'd suggest Rosco's Milford Sound Sea Kayaks Naturally. Great experience, beautiful scenary, great guides, and Rosco has quite the personality.
Just did the Routeburn Track with Ultimate Hikes. Great experience. They take great care of you.
Glenorchy is beautiful. If you're into wine, Peregrine Winery is a nice stop and great Pinot Noir.
If you're into the bar scene, there are tons of them in Queenstown. There are a handful known as the "good bars", all w/different names. They're a bit more high end, but really nice environments. I think their trademarks are huge fireplaces.
You might also want to check out Backstage Pass New Zealand if you're looking for a personal guide service. They can put you onto some great fun!
Have a great time!

My kids' all-time-favorite pizza place is in Queenstown....Winnie Bagoes! In the pedestrian shopping area. I think we ate there 3 different times! Loved sitting upstairs on the little balcony and watching all the people below.

We loved Queenstown. Have fun!

If you are visiting Queenstown, keep an eye out for the giant kiwi, said to lurk down by the edge of the lake. On my last visit to this beautiful vacation spot, I tangled with this aggressive character, and have the following photographic evidence to prove it !
http://www.flixya.com/photo/347983/G...town_New_Zeala

Just so everyone knows, flixya is a site that pays the poster if someone clicks on their link.