Here is a list of some of the most notable titles that Valve has worked on:

1. Half-Life (1998)
2. Half-Life: Opposing Force (1999)
3. Half-Life: Blue Shift (2001)
4. Counter-Strike (2000)
5. Team Fortress Classic (1999)
6. Day of Defeat (2003)
7. Half-Life 2 (2004)
8. Counter-Strike: Source (2004)
9. Day of Defeat: Source (2005)
10. Half-Life 2: Episode One (2006)
11. Half-Life 2: Episode Two (2007)
12. Portal (2007)
13. Left 4 Dead (2008)
14. Team Fortress 2 (2007)
15. Left 4 Dead 2 (2009)
16. Portal 2 (2011)
17. Counter-Strike: Global Offensive (2012)
18. Dota 2 (2013)

Valve has also contributed to the development of other games, including Ricochet and Deathmatch Classic, as well as the development of the Source engine, which has been used to create many games beyond Valve's own titles.
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