League-of-legends – Season end dates and rewards

The League of Legends Wiki lists all of this. A table for the rewards for kills is shown in their Kill article, which I will mock-up below. Note that as of V1.0.0.152, the bounty values were reworked to increase the effect of each kill or death. The table shown below reflects the current bounty rewards as of said patch.

K/D Count = Killstreak/Deathstreak count for the champion slain
K Reward = Improved reward for killing a champion with that kill streak
D Reward = Reduced reward for killing a champion who is getting hosed

K/D Count | K Reward | D Reward
----------+----------+---------
    1     |   300    |   300   
    2     |   360    |   260   
    3     |   432    |   182   
    4     |   500    |   127   

The Kill article notes that a first blood has a +100 gold bonus, so the first blood will always be +400 (as this question leads me to believe that executions don't increment your death streak).

The other point to take home is that multi-kills and aces do not provide any bonus. Likewise, getting a killstreak doesn't get you any additional reward, only the person who finally takes you down.

The article for Assist states that there is a pot of 70% of the kill bounty that is split between all champions that provided an assist for a particular takedown.

The following forum thread (in date of the Feb-08-2012) states that :

In keeping with this objective, we’re going to begin distributing some rewards to our new players to help them on their way to level 30. Once a new summoner reaches level 3 they will receive 400 Riot Points as a reward for their participation and perseverance up to that point. See [1]

Other accounts have received these 400 RP in december [2].