Check out this looong list of achievements at; 

http://www.addictgaming.com/story.php?id=239

Images have surfaced today of new Halo 3 achievements, they are from PAX and people who could be bothered to explore their dashboards at the Bungie booth. It is still unclear how these achievements will be added to Halo 3 but I would say it has something to do with the Mythic picture we posted a few days ago. One thing is for sure though, soon bungie will have a lot of explaining to do. It seems an additional 30 achievements have been added going by the "79 of 79 Unlocked".

I know something big is coming but i don't think it's DLC as they only bring 250 more points and this has way more.

As someone who has the full 1000, i can't wait to get these new achievements.

Oh great, I can't wait to see how much this is going to cost. Why would they fit 30 achievements into 250 points? That's a little more than 8 points per achievement. They wouldn't make them all so small so I have to agree that it's not regular DLC.

WTF ????
completed Halo on 4-player Legendary LIVE-co-op, with Iron, and everyones in ghosts
0G ???????

sweet!! still haven't gotten all the achievements for halo 3 (marathon man :( ) I think something big is on the horizon for halo.

@ erikers
It seems that they want to fit 30 achievements into 750 Gamerscore.
That would be an average of 25G per achievement.

Whoa!
I already have 1000 achievements for Halo 3,
This should be interesting!

I'm only at 475/1000... I got to hussle and get the rest

20 x 10G = 200G
10 x 5G   =   50G
---------------------
30               250G
Sounds about right! WRONG! lawlawl

Didn't check the link!

Time to get back on the grind!

This is awesome. I wonder what it will be. I am very intrigued.