First, before we bring back any titles, I think they need to get unify the World Titles. Even if they started re-enforcing the brand split, there should be only one WWE Champion, with all other champions being regarded as close seconds
Now, for belts to bring back...
WWE Light Heavyweight Championship.
The Light Heavyweight title needs to be brought back, except that I don't want it as a low card belt. I want main eventers and upper-midcarders who happen to be under the title's weight limit (i.e. Cody Rhodes, The Miz, Dolph Ziggler) carrying it around and treating it a like big deal. The reason I chose the Light Heavyweight title over the Cruiserweight title is simply because the term "Light-Heavyweight" sounds a bit more prestigious.
WWE Hardcore Championship
However, I do not want them to use the WWE version of the belt...
I would rather they adapt the WCW Hardcore Title design.
It looks more like a championship title, and thus symbolizes scratching and clawing to reach a big prize. I would ditch the 24/7 rule, as it devalued the title. It may be impossible to do real hardcore matches in the PG era, however, we've seen wrestlers do pretty decent "Street Fights" in recent years, as well as "No-Disqualification" and "Falls Count Anywhere" matches. Not to mention gimmick matches such as Cage Matches and Table Matches. It would be nice to center those things around a championship. The Hardcore Championship will allow your low card guys to pay their dues and get over as tough guys. You can also give this belt to high fliers who wouldn't be able to compete in the light heavyweight/cruiserweight division due to their being over the weight limit (i.e. Alex Riley, JTG). The midcard can carry the load of gimmick matches, and you can spare your top draws from having to risk serious injury.