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The Silver-Tongued Devil achievement for Fallout 3 is worth 20 G

To get the achievement you have to win 50 speech challenges.

There is a girl in Little Lamplight called Knock Knock. If you follow the conversation that starts with how she's in charge on morale, she tells you a joke. You can lie to her and tell her how great you think the joke was, which is a speech challenge, which like the one in Big Town can be repeated infinitely if you want to.

The dialog is a little longer than the Bittercup/Pappy exchange in Big Town, but less problematic to get to work.