Other sites like humblebundle?

This

This too to be fair it IS steam, but think of the savings ^^

Bundlestars often has good bundles. It's like Humble jr.
Indie Gala is very hit or miss. More often miss.
Groupees is like Gala.
DIG often has a lot of trash in their bundles as well, but tend to be really really cheap, and sometimes you'll get something good.

That'st he common ones. Then there are a couple of lesser known bundle sites, like Flying Bundle & Lazy guys