The average discount is only about 50%, but Sega games having the largest markdowns of around 80%. However, pages of games are on sale and I am wading through looking for the best bargains. I don't know if they have any coupon codes working at the moment.
Company heroes 1 Complete $7 http://www.gamersgate.com/DD-COHC/company-of-heroes-1-comple…
Operation Flashpoint Complete $7.50 http://www.gamersgate.com/DDB-OFC/operation-flashpoint-compl…
Realms of Arkania $5 http://www.gamersgate.com/DD-ROABOD/realms-of-arkania-blade-…
Timelines: Assault on 'Murica $3.75 http://store.steampowered.com/app/234060/
Total War Grand Meister Collection $52.50 http://www.gamersgate.com/DDB-TWGMC/total-war-grand-master-c…
Don't forget, you can get Blue Coins for doing reviews and simply just ranking a game. It shouldn't take too long to be able to get a discounted DLC for free.
Thanks! Ended up getting Castle of Illusion for $3.75 :) Great deal!