Fish that I have been able to successfully keep with tiger barbs, that also will do well in a tank your size:
Golden Barbs
Cherry Barbs
Yoyo loaches
Red tailed black shark
Albino Corys (if the corys did not have lots of good hiding places then the barbs would chase them time to time)
Bronze Corys
Pepperment Corys
Glowlight Tetras
Serpae tetra
Sailfin Pleco
There are many more fish you can keep with tiger barbs, these are just fish that I have kept with mine over the years. When I think of the rest I’ll add them.
EDIT: Having thought about it some more I would not recommend the albino corys, overall mine did well, but for some reason the barbs loved to search the tank for them and chase them out of there hiding places.
I was alos albe to get rummy nosed tetras with my tiger barbs.