I) 'Hulkbuster' Iron Man vs The Hulk
Oh c'mon Marvel, I've been waiting years for this. The Hulkbuster Armor is one of the most popular sets of armor for Iron Man and for good reason. It's just badass. Part of the fun of the first film was seeing these guys/girls tangling together. The fight in the forest, was simply epic.
Obviously they worked out their issues and worked together to beat the Chitauri; but I still want to see these two heavyweights go head-to-head. Maybe Tony just wants to have an armor that can help him go toe-to-toe with The Hulk, not in a way that's overly dramatic; just a sparring match motivated by Starks cockiness and narcissism. A hard hitting battle that would be just as epic (if not more, depending on your tastes) then the Thor vs. Hulk fight from the first film.
TS: I need you to suit up, I have a toy I've been working on
BB: You have a death wish?
TS: No, just a really nice piece of armor that I'm itching to put on
BB: You know I won't hold back
TS: Please, don't.

II) Project Pegasus (Quasar & Ms.Marvel)
The Avengers showcased how SHIELD is not the penultimate secret organization. They do answer in part to 'The Council' now I'll be honest, when I watched that I started thinking of Quasar, Ms. Marvel, etc. If Marvel were to have 'The Council' be Project Pegasus, they'd have opportunities to introduce all these characters. Which lets be honest, with Thanos looking like the villain in the sequel; they'll need all the help they can get and Project Pegasus is in many ways the SHIELD of the Marvel Cosmic Universe.
Doesn't hurt that IM2 and the comic prelude to The Avengers references Project Pegasus ;)
III) Ant-Man and The Wasp.
OK, so can we all just agree that these two (or maybe just Ant-Man although I doubt it) will appear not only before the sequel to The Avengers, but of course in the sequel. These two sort of need to happen after all the rumours and teasing. Feige is teasing that Ant-Man is close to happening and Marvel has the space for an Ant-Man movie. Make it happen Marvel!
IV) LMD
Life Model Decoys are a SHIELD staple, and I was surprised that we didn't get to see it in The Avengers. With Banner and Stark helping SHIELD out, you'd think they'll help SHIELD by developing a basic decoy for them.
V) Doctor Strange
I said this before in my article
Why The Avengers 2 may be a letdown but here's my dream cast that I detailed in that article.
Idris Elba as Black Panther
Patrick Wilson as Ant-Man
Zooey Deschenel as Wasp
Ed Harris as Red Hulk (Rulk)
Tom Hardy as Moon Knight
And...
Jean Dujardin Cannes as Doctor Strange
Looking back, I can't imagine Rulk or Moon Knight appearing for awhile, but the others I still stand by. Especially Jean as Doc Strange; which the idea came to me as my girlfriend dragged me by the ear to The Artist. After watching the (great, if pompous) movie, I realized that Jean would be perfect for Doctor Strange. Anyone who's seen The Artist would be inclined to see my point of view. He has swagger, charm; and just this classic look.
VI) Thanos
Yes!
Yes!!
Yes!!!
Thanos was an addition by Whedon, and his insistence certainly can't be just for shock value. He has to be the villain of The Avengers in the sequel. He has the power to destroy planets, and doesn't need an army really to fight The Avengers.
In The Infinity Gauntlet, many of earths heroes are killed by Thanos literally snapping his fingers. So imagine the possibilities. I'd love to see this remove a few characters from the mix. I can't really say who, but it'd give a chance for new characters to be added while having a balance between it all; which as The Avengers showcased, is important.
BONUS: What I don't want.
- Give Loki a break
- Don't even touch Civil War
- Any other Director aside from Whedon. At this point, he is the man for the job! I'd imagine they'd keep him (Since he's helped give Marvel all that $$$)