Red Dead Redemption:
Friends in High Places - Use a pardon letter with more than $5000 bounty in Single Player. - 10G
I got this a few days ago. It was the last one that I needed to get all the achievements, 1100/1100. It's one of the easiest to get from RDR's list. All you really have to do is go to a big town, Armadillo or Blackwater, find a good place to haul up and kill all the Cops. Once they are dead, save and move on to the next town.
Also, if you're doing the Advanced Co-Op maps, time doesn't mean anything. Just keep getting headshots, with chains, and the money will grow quickly giving you Gold medals. Also helpful if one of your squad mates has a Sniper rifle.
Monkey Island 2: SE:
Largo Embargo Complete - Completed Part One: Largo Embargo. - 25G
I downloaded this, and the first one, at the same time. Finished the first on Saturday and have just started to play the second. Loving both of them, and the second really has made some improvements from the first. But it was annoying to find out they have changed the controls round a bit. But I got used to them.