Contributor

...Contribute? For the value, click here.

Give a game! And the value is based off US version of steam store pricing (base value, not sale value). Bundle games are capped though, and you can find out if a game is bundled by checking here

you have to give games, and the value is calculated on the value of the game in the steam store at the time of the giveaway. Bundle games work differently, you can gain up to $30 contributor value with bundle games and then you gain less from these games.

I suggest to start to read the FAQ first

You giveaway games to get contribution value.

The value you get is the normal US price of the game. If the game has been on any bundles at all the value is reduced. This works along the line of:
[Total Non Bundle Game Value]*0.2 + $30 = total value of games that have been on bundles at some point.

So for example someone gifts $100 of games that haven't been on bundles can gift $50 worth of bundle games and get the credit for it. If they gift more than $50 of bundle games, that extra value is locked away and can be unlocked by gifting more non bundled games.

EDIT: Here is the list of all games that have been on bundles (indie bundles / humble bundles / humble weekly sales etc.)

TY everyone