Every game in a Humble _Indie_ Bundle has always been available DRM free. Titles in their "Humble Trove" (a monthly subscriber perk) are also DRM free. Other bundles Humble Bundle sells are often Steam only.
I find it slightly sad that Humble Bundle watered down their brand by allowing Steam-only sales in the (Not So) Humble Store, then further by increasingly having Steam-only bundles.
I've bought two ebooks from there for $5 each and I think they are worth it. You can read them online you can make bookmarks and also it preserves your reading progress or you can download a .pdf / .epub. I haven't found a better / cheaper resource for learning new technologies.
P.S. The books I bought were for Golang and VueJS.