I've just started playing League of Legends, so I'm getting plenty of first hand experience with being dead. However, I haven't figured out what determines the length of time I spend in limbo, does anyone know the time amounts and/or the formula to determine how much time my X number death will cost me?
Champion level and time spent in the game are the main factors - longer games = longer death timers; higher level = longer death timers.
On Summoner's Rift time spent dead scales from 12-50 seconds as Wiki says.
There isn't a calculated formula for champion death time, at least not one known by the players.
There are some ways to reduce this time. Utility tier one mastery Good Hands reduces death time by 4% / 7% / 10%. Each Quintessence of Revival reducse death time by 5%. There is also the summoner spell Revive which instantly revives your champion.
Different maps have different death timers as well. From shortest to longest: