I'm in transit from L.A. to Bangkok, stopping for three hours in Taipei. I went to Dian Shui Lou, which is near the C departure gates in the international terminal and had truly excellent xiao long bao. The wrappers were thin but quite sturdy, holding in plentiful amounts of extremely flavorful soup. The filling was just about perfect, complex with light flavors that enhanced the porkiness without distracting from it. There are only five to an order and they aren't particularly cheap - one order and an iced coffee came to US$9.50. Still, having just come from LAX, which has possibly the very worst international departure terminal - especially once past security - that I've ever been subjected to, this was a very big plus of a layover. And I'm fussy about my XLB. I've had them all over China (including those made by friends mothers and grandmothers), other parts of Asia and in Los Angeles - where there are a number of good options.
Also, I stopped for a bit in the Evergreen Lounge - the EVA Airways business class lounge - and had what was one of the very best espressos that I have ever had in Asia. (I'm also fussy about espresso.) It came from a well tended machine and I guess the coffee they use is particularly good, but it was very strong - as I like it - and not at all bitter.
I'm going to have to transit through Taipei more often.