Invaders 1975

Before the Avengers Captain America belonged to another group during World War 2, the Invaders, the team consisted of Captain America and Bucky, the Sub-Mariner,the android Human Torch  his sidekick Toro and the British heroes Union Jack and Spitfire. The stories revolved around them fighting the axis forces and their super powered beings.

The Invaders ended it's run in 1979.

What If 1977

What if dealt with stories in the Marvel universe if a certain thing either an event or characters history went a different way, The Watcher was featured who set up the stories, telling some backstory on how it happened on the mainstream Earth then showing a parallel one where at a certain point either due to a character changing their mind or actions that  history diverged on a different path. Some examples like the picture above if Spiderman joined the Fantastic Four or Steve Rogers never was awaken from being frozen in ice etc.

The comic had two runs, the first ended in 1984 and he second run went from 1989-1998.

The What If series is available on Amazon.
What If volume 1

The New Teen Titans 1980

The original Teen Titans comic appeared in the 1960's and featured the sidekicks of major heroes, Robin,Kid Flash,Speedy,Aqualad and Wonder Girl, basically a Junior Justice League. The book wasn't a major hit.
In 1980 Marv Wolfman and artist George Perez decided to revive the team, they had 3 original members, Robin,Wonder Girl, Kid Flash adding new members Beast Boy from the Doom Patrol who went to the code name Changeling and three newly created characters the half demon Raven, Cyborg and the alien Starfire.
The New Teen Titans became a runaway hit in the early 80's, something DC really needed with Marvel dominating the sales charts with X-men and their other X-titles. Teen Titans is still being published but with roster changes and with the New 52 in 2011 a new history.

The 80's New Teen Titans is available on Amazon.
The New Teen Titans

Weird War Tales 1971

A DC title Weird War Tales in each issue featured war stories with a horror theme, the stories were hosted by a skeleton ( I am assuming it was supposed to be Death/Grim Reaper) clothed  in different military garb for each tale.The series run lasted till 1983.

Marvel Two-In-One 1974
Like Marvel Team-Up with Spider-Man this featured the ever lovin' blue eyed Thing partnering up with other Marvel heroes and an assorted variety of other characters to fight evil or maybe locate a good poker game, I would assume these adventures occured during his Fantastic Four downtime. The series run ended in 1983.
The classic Marvel Two-In-One is available on Amazon.
Marvel Two-In-One

 

Rom Spacenight 1979

Rom was a comic tie in to sell the Rom electronic toy from Parker Brothers, but it went on to last a lot longer than the toy, the series had Rom coming to Earth to persue his enemies the shape shifting Dire Wraiths, an offshoot of the Skrulls. At first it seemed Rom was killing innocent people, eventually the truth came out which led to a Rom joining other Marvel heroes and S.H.E.I.L.D fighting the Wraiths.  The series run ended in 1986.

Rom toy commercial

Marvel Team-Up 1972

From Marvel this comic would team up Spider-Man with another member of the Marvel roster or even tv characters like the issue above with the Saturday Night Live (Not Ready for Prime Time Players). Basically like the Brave and the Bold team up comic with Batman from DC. The original run was till 1985, and a favorite to pick up if your were a Spidey fan back in the day.

The past issues are available in volume sets on Amazon.
Marvel Team-Up with Spider-Man