There are so many possibilities within TCC if you look around and think for yourself that you don't really need to go further afield. Apart from ground fighting, as Rob says, for which TCC offers many excellent ingredients but definitely not the way to 'cook and serve' when you're down there on the ground. The problem is, most individual tai chi lineages/schools tend to focus on a relatively narrow range of options and qualities, presumably in order to go deeper into a more narrow set of parameters in order to achieve a specific kind of excellence. This is of course the more optimistic or charitable view
. Even within the "push hands" envelope there are so many possible useful variations: in kinds of techniques (only push, or also strike, lock, throw), kinds of steps, more fixed formats or free flow, variations in speed, variations in 'aggression'. And above all the spectrum between explicit use of structure, rooting and 'solidity' and radical use of total yielding (more like Tao Ping-Hsiang or Peter Ralston), and increasingly being able to combine both, sometimes simultaneously. If one trains lots of these variations in a considered way, always looking for the underlying consistency of principles, then this will develop a strong and flexible body and mind. Plus use of objects/weapons, as Charles mentions.
Apart from that, when it comes to other disciplines: time for another Contact Improvisation vid:
https://www.youtube.com/watch?v=XUe2IZ3-D4s