Kosmos two-player series
The Kosmos two-player series of games (the "Spiele für Zwei" in German) contains many popular, quality two player games that are, for the most part, easy to learn and play. The games in this series often show up in "What to Play With Your Spouse" GeekLists on BGG. Their small box also lends itself to portability. Many of the series have been published by Rio Grande Games except where noted.