Foundries are pretty good overall and the route there takes you through bonuses to HI / HC and discipline which you probably want anyway.
There's also a short route through the other side of the mil tree through to Professional Training which gets you 10% discipline for 4 inventions, which is quite significant if you're going to be doing a lot of early warfare.
Great Temples and Grand Theaters are must haves even if you're not trying to mass convert as they both provide 5% civ level and 10% happiness to integrated / same religion pops for a single building slot. Which is basically equivalent to 15% output or more, each, unless you're already hitting the happiness cap. Open Religion in particular is so close to the top of the invention tree that it's hard to resist getting on day 1, and it's right next to a nice research efficiency bonus too.