At the moment the Flash is becoming one hell of a show. The show will be renewed for a new season so could that mean Barry gets a sidekick. I'll be going through a few possibilities of who they could be.
This is probably not a likely candidate for Barry's sidekick but it would be cool to see him. Wally West is the first sidekick of Barry and got his powers by recreating the accident that turned Barry into the Flash. Although a cool character I think it'll be unlikely for him to join the show.
Bart Allen is the grandson of Barry Allen. Impulse is from the 30th century and he travels back in time and meets he grandad. I think now that time travel has been introduced to the show he would be a good edition to the flash.
This is probably the most likely character to appear on the show. Cisco Ramone is already a key character in the show and I think that he'll become Vibe in the not too distant future.
Killer Frost is the most unusual character on this list. Although unusual she could appear in the form of Caitlin Snow. This could happen but Killer Frost is known as a villain and not a hero so Caitlin would have to have a change of heart.