Dungeon Siege Bundle - $11.99 (All Steam)
1. Dungeon Siege
2. Dungeon Siege II
3. Dungeon Siege III
4. Dungeon Siege III - Treasures of the Sun
Command and Conquer The Ultimate Collection - $16.99 (Origin)
I know for awhile people kept buying Steam's DS3 just to get them (and Steam kept the price for it artificially really high compared to other outlets).