This (now defunct) question came up on Stack Overflow a while ago. While Python is noted for its use in many games, here's a list of professional-quality games that use Pygame:

Dangerous High School Girls in Trouble is a 2D RPG by Keith Nemitz that was nominated for a Writers Guild Award, won "Most Innovative Game" by the Casual Games Association, and was also selected as a finalist for the 2008 IndieCade Festival of Independent Games. It is available for purchase off of Steam. Gameplay video

Analogue: A Hate Story is a visual novel-style game that was a 2012 IndieCade Finalist. As of December 2012, Analogue has sold at 40,000 copies. Steam store link (with videos).

Unity of Command is a turn-based, operational-level wargame that covers the entire 1942/43 Stalingrad Campaign on the Eastern Front. Trailer video. Available on Steam.

Frets on Fire is an open source Guitar Hero clone. Gameplay video

7 Grand Steps is a board-like puzzle game from Keith Nemitz of Mousechief and is a 2013 Independent Games Festival finalist. Trailer video

Metin2 is an Oriental-themed action MMORPG. Trailer video

Galcon 2 is a high-paced space shooter game. Gameplay video

The Witch's Yarn is an interactive story game from Mousechief. Gameplay video

While not a game, someone has mentioned that the Minecraft editor MCEdit uses Pygame. MCEdit tutorial video

UPDATE (2022/02/20): Added Friday Night Funkin to the list.

UPDATE (2020/11/01): Codename Mallow is a multiplayer fighting game written in Python.

UPDATE (2018/9/21): I've also found Super Potato Bruh, a challenging platformer that appears to be in the same vein as Super Meat Boy.