At a glance, the selected apps from Ubuntu App Showdown 2012 are:
- Stormcloud
- Nitro
- Steam for Linux
- Geary
- InSync
- Lightread
- UberWriter
- Unity News Lens
- CuttleFish
- Postman
I agree with most of the entries other than Postman. Given some relaxation on just 2012, my choice would be the highly useful Jupiter which existed before but got revamped and subsequently much attention in 2012.