The Rare team was spun out of Microsoft. They were the video game company that Microsoft bought from Nintendo. They were responsible for Golden Eye, Conquer, and Perfect Dark.
I'm not sure if this would be considered a successful spin off though as Microsoft bought them when they were, IMHO, at their peak.
I would not count Rare as a good acquisition: Microsoft bought them for $375M, and they haven't produced a single hit since. To put that in perspective, Bungie (a much smaller studio than Rare at the time) was acquired for less than $40M, and their games and IP generated over $1B (and counting) in revenue for Microsoft.
I'm not sure if this would be considered a successful spin off though as Microsoft bought them when they were, IMHO, at their peak.