Some deep discounts on at least a few linux-compatible titles:
X-Com Enemy Unknown Complete $25.00
Europa Universalis IV Digital Extreme Edition $11.24
Pajama Sam - No Need to Hide When its Dark Outside $1.74
Cities in Motion Collection $12.49
Freddi Fish and the Case of the Missing Kelp Seeds $1.74
Knights of Pen and Paper +1 Edition $3.74
It's been a while since I've purchased a game from Amazon but I know at least some (most?) of the titles come with Steam keys (DRM: Steam under the title). I don't know if steam keys can be obtained for the drm-free versions--please use due diligence and research before buying.
EDIT: Newegg has Enemy Unknown for $7.50
Enemy Unknown is on sale for the same price as EW at Amazon ($9.89). The Slingshot and Elite Soldier Pack DLCs are still full-priced ($7 and $5, respectively).
The Complete Edition is available for $33.48, but that is slightly more expensive than buying all pieces separately.
$9.89 (EU) + $9.89 (EW) = $19.78
$6.99 (Slingshot) + $4.99 (Elite Soldier) = $11.98
$19.78 + $11.98 = $31.76
For comparison, here are the prices from a sale 6 days ago.