The Flash spins out of Arrow as Grant Gustin first appeared on Arrow as Barry Allen, and we also got to see the accident which gives Allen his powers. The CW also filmed the pilot, which revealed a first look at The Flash costume as well as set images and video.
Here are the descriptions from CW for The Flash and iZombie:
Barry Allen is a Central City assistant police forensics investigator who arrives in Starling to look into a series of unexplained robberies that may have a connection to a tragedy in his past. A comic book fanboy, Barry is obsessed with the Arrow unaware that working with Oliver and Felicity to solve the crime has brought him right into the dangerous world of the vigilante.
CAST: Grant Gustin, Jesse L. Martin, Rick Cosnett, Danielle Panabaker, Candice Patton, Carlos Valdes, Tom Cavanaugh, John Wesley Shipp, Michelle Harrison, Patrick Sabongui
A med student-turned-zombie takes a job in the coroner’s office to gain access to the brains she must reluctantly eat to maintain her humanity, but with each brain she consumes, she inherits the corpse’s memories. With the help of her medical examiner boss and a police detective, she solves homicide cases in order to quiet the disturbing voices in her head.
CAST: Rose McIver, Malcolm Goodwin, Alexandra Krosney, David Anders, Robert Buckley, Nora Dunn, Ruhul Kohli