Why does a .io TLD make you think about API access?
http://www.russellbeattie.com/blog/artisanal-websites-the-ri...
(Beattie credits evocative short name, stable British administration, lots of available short and English word domains.)
Another clever new-ish one is .ac, but it's more expensive than the already expensive .io.
.io domains are very popular in a ton of different areas, though!