I see some very promising trends in some of the Western Zen stuff, eg Brad Warner ( http://hardcorezen.blogspot.com/)(before anyone says it, I also see big problems with him!)

There's a lot of dumping of mysticism, and some of the more unfortunate bits like gods and reincarnation.

And there are Buddha quotes like:

"Be lamps unto yourselves. Be refuges unto yourselves. Take yourself no external refuge. Hold fast to the truth as a lamp. Hold fast to the truth as a refuge. "

(intermediate source http://www.sapphyr.net/buddhist/buddhist-quotes.htm, I'm pretty sure there are primary sources but too lazy to dig them up)

Which I think is very compatible with rationalism.

And a lot of Buddhism seems to me to make nice testable claims "do these things and you will experience a greater frequency of desirable mental states", for example.

However there's also other stuff I'm somewhat sympathetic to, but have doubts about, which seem to suggest giving up on rational thought.