A few core modules that were buggy but are solid now:

Promotions and coupons
Taxes
Payments (supports 30+ payment gateways!)
Products
Orders

As an added bonus, the Commerce Shipping module that Acro Commerce helped develop received a full stable release alongside Commerce 2 (which is especially cool when you remember that Commerce 1 launched with no shipping functionality at all). Commerce Shipping features a much-improved API and includes support for UPS and FedEx, with USPS to follow shortly.

Acro Commerce and other community members have been working on a few other associated modules to go along with the Commerce 2 launch. Here are the details:

Point of Sale is going to alpha release.
Commerce Migrate is going to have a new release (likely not a stable release, however, as there is still work to be done migrating edge cases).
Ubercart to Commerce 2 migrate is mostly done and includes all core stuff like products, customers, orders, taxes, etc.
Commerce 1 to Commerce 2 migrate is a little rough but is still very usable; an improved version should be ready in October sometime

A cool new Composer-based Commerce Kickstart installer is also available! It represents a great improvement over the original Commerce Kickstart and should be easier for everyone to use.

TLDR: The fully supported, stable release of Commerce 2 is live and has lots of cool stuff with it. If you were hesitant to use it to build sites before, you most certainly can go ahead now.