I don't know how many of you know this, but if you use your account on Waypoint you can create your own custom Challenges (which DO reward you with credits). You can also invite friends to do these challenges but they can only see them if they check for them on their custom challenges page.

Custom Challenges include: Campaign challenges, Multiplayer Matchmaking challenges, Firefight challenges and Custom Game challenges (although the Customs don't reward nearly as much as the others).

I haven't experimented with the Campaign or Firefight challenges but I know that there are four different types of MM challenges to choose from:

- Kills
- Headshots
- Wins
- Medals

I have three going right now (I didn't invite anyone else to do them, sorry).

1) The Reaper (You get to name them btw ) - 200 Kills, 24 Hours to try, and 4715 cR reward.
2) Winning . . . - 15 Wins, 24 Hours to try, 3536 cR reward.
3) Paint the walls red - 100 Headshots, 24 Hours to try, 4715 cR reward.

Link for proof (if it will let you enter the page): http://halo.xbox.com/en-US/Career/haloreach/Challenges

This feature will most likely also be in Halo 4, so what do ya say guys? Let's help eachother rank up