When Draper and his colleagues at Sterling Cooper have to write a memo or sign a check, they often use pens from the A.T. Cross Company. The Rhode Island-based pen manufacturer paid for its products to be used on-set during the series, while teaming up with AMC for ads on-air, online, and in retail stores that sell Cross.
The company was one of Mad Men's original partners from before the show's first premiere, but its ongoing presence onscreen has been a less obvious product placement than some of AMC's other partners. The next episode you watch, keep an eye on those advertising scribblers -- what they write could be advertising gold both in their world and ours.
Clarification: An earlier version of this story said Cross paid for placement. No cash was exchanged. AMC and Cross did a cross-promotional barter instead.