The Astros have signed first round pick George Springer, according to John Manuel of Baseball America (on Twitter). It's a $2.525MM deal, according to Zoodig on Twitter. Legacy Sports Group represents the outfielder, who was the 11th overall selection in the June draft. Houston also signed third rounder Jack Armstrong Jr., according to Manuel and Brian McTaggart of MLB.com reports that Armstrong obtained a $750K deal (Twitter link).
I spoke to Springer before the draft and you can check out the interview transcript here.
You can keep track of which top picks have signed with MLBTR's list.