Number one: Mace Windu.
One of the most crucial moments that led Anakin to become consumed by the dark side of the force was when he halted Jedi Master Mace Windus attempt to kill Darth Sidious by cutting off his hand. After Sidious makes a huge comeback from lying on the floor to a old man with "unlimited power", the last we see of this famed Jedi master is his electrocuted corpse flying out of the chancellors office window. Now, we presume he is dead, since we never hear about him again in the movies or in the expanded universe. But what do we really know? Would such a talented, skillful master go out just by being flung out of a window? Now of course, people here do not have enough influence with the force to survive that, since our midi-chlorine count is far to low, but this is a Jedi Master! Not just a random Jedi waving his light saber keeping justice, this is one of the most powerful Jedi, only second to Yoda! In many of the novels about the Clone Wars, Mace has gone through a lot worse and survived despite all odds! He single handily took out a seismic tank, survived the explosion of a colossus machine called... well, the colossus, and also a whole load of other ordeals. So this isn't to say he is a wimp for dying by just being thrown out a window, this is opening a possibility for Episode 7 to take up! Think of it: one of the most mysterious, bad-ass Jedi makes his return in the newest Star Wars installment. How cool would that be? Because Mace is a Jedi master, he has a stronger influence on the force then other Jedi ranks, so its completely possible he was able to force-cushion his fall. Also, he could come back with a mechanical hand like Luke's, so there can be a point of comparison between the two Jedi.Now of course Mace will have aged quite a bit, but just think of how epic the newest Star Wars will be if we get some characters back in the game. ESPECIALLY the kick ass ones.
Number 2: Obi-Wans Daughter
Ok, now this one may require some reasoning. At the end of Episode 3, its apparent that Obi-Wan and Yoda re-transmitted a message from the Jedi council warning the surviving Jedi to stay away and to go into hiding. Because the Jedi are now underground, does this mean they still follow the Jedi code? There have been instances in the novels that tell the events in between Episodes 3 and 4 where surviving Jedi abandon their attachment to the Jedi code and start developing a new life. Couldn't Obi-Wan have done this when he seeks refuge on Tattoine? He was still young and in his prime so surely he could have attracted some female spice trader or pilot and started a family. What if he was to have a daughter (or possibly son, but the saga could use more females) that could have followed the path of Jedi knight Sharad Hett and grow up among the Tusken raiders? For all we know in the movies, tusken raiders are a band of merciless desert wanders. But what if we see a new side? In the expanded universe books, we see how Hett grows a attachment to the sand people, but we never see that in the movies. What if Episode 7 brought something new to the table? What if they where to bring in a new perspective on this desert tribe, while also bringing in a new type of Jedi?
Number 3: Boba Fett returns.
Almost every Star Wars fan knows that Boba Fett survived his encounter with the Sarlaac pit in the expanded universe comic books, and also know that Fett is one of the most bad ass people in the Star Wars universe. We saw him track down Han Solo in Episode 5, trap them in Cloud City, we saw his bad ass armor and his bad ass ship and heard his bad ass voice. Almost everything about Boba is bad ass, minus the way he dies. Many people where disappointed by this famed bounty hunters death when he fell into the Sarlaac pit after a blind strike by a blinded Han Solo. Although we under stand he survived the his ordeal in the expanded universe books, it would sure be a good stroke of nostalgia to see him back in action in the new Star Wars Episode 7. In fact, wouldn't it be the most epic thing if Mace Windu AND Boba fett returned? That way there would be a side conflict going on with Boba trying to kill Mace for killing his dad, Jango. And also, Boba never really found out about Maces death in Episode 3, so it could have been a long standing search. Personally, I think that might be one of the most interesting things to see in Star Wars Episode 7.
So what do you think about these story lines? Have something better? Go ahed and jot it down!