My fish are listed at the bottom of my signature.
Serpaes are cool looking fish, I had a couple of them a while ago (died during ich outbreak)... they're also very hardy (though not hardy enough to outlive ich, I guess).
If I were starting a new 30 gallon, I'd probably have pretty much the same fish as I do now, I really like the tiger barbs, they're so active (I plan to get a few more, once I can find ones that are approx the same size as my current ones).
You are cycling with zebra danios, they're very hardy fish and I would bet money that they'll come out of the cycle just fine. As you've noticed, the zebras stay 99% of the time at the top of the tank, and that's cool because very few fish stay so close to the top most of the time (except for bettas, but they can't be in a tank w/ serpaes).
Here's what I'd do w/ your tank:
4 zebra danios
Assuming they all make it thru the cycle... if I were you, I'd get a few more to make a total of 6 (once cycling is complete).
6 serpae tetras
6 cherry barbs
Tiger barbs would probably be too nippy to the tetras, or maybe even vice-versa, ime - though someone here may have had a different experience.
4 cories
Or 6 if you can find the 'dwarf' cories. Supposedly they are bottom dwellers, but my guys zip all around the tank. But they are invaluable when it comes to cleaning any excess food off the bottom!
Good luck, and have fun deciding what to get!
~Tara