Lots to choose from in the Steam sale. Stardock has games and software in the sale for some great discounts.
Save up to 75% on Stardock Games and Software During the Steam Winter Sale » Forum Post by Tatiora
Games highlights:
Star Control: Origins
Galactic Civilizations III w/ expansions ...
You would just need to buy one of the gold bundles. It gives Steam keys for each individual items, so you would just end up with an extra base game key.
Not on sale, but if you did purchase Total Annihilation in the previous sale it has been updated with the Battle Tactics expansion. Free update via Impulse. :)
Paradox is one that will be using GOO going forward, and other devs/pubs will also be using it going forward, although I can't say if every title will have it.
I'm going to mention that GOO should be listed on the product page, as I agree it would be useful for people to know. Thanks!