Humble Bundle's May 2017 monthly bundle has just been revealed, which also prompts the announcement of the headline game for June 2017. Subscribe now (or pay early, for existing subscribers) for instant receipt of a Steam key for Stellaris. When the full bundle is revealed at the start of June, you'll receive a further seven games (most of which should come with Steam keys).
The base price for the bundle is $12.00, which currently works out at £9.26 (note that if you pay by PayPal, their currency exchange fees will increase this slightly). For new subscribers, if you've recently purchased one of the weekly bundles, you should be eligible for a 10% discount on the first month.