Travel from Siem Reap (Cambodia) to Bangkok (Thailand) could take you the whole day (by bus/train). I'm wondering if there is any sightseeing between Siem Reap and Bangkok where I can stop, sleep one night and then continue my travel. The idea is split the trip in two parts, but staying in a place where there is something to see/do.
There is no convenient midpoint stop, I think it's better to just bear the long road journey (I hear it's better in 2012 than few years ago).
Chachoengsao has a huge buddhist temple (allegedly the largest in the world), an old market and a decent river tour. Worth a visit, technically on the way, but rather close to Bangkok (1-2h).
Poipet is a seedy border town which may appeal if you're into casinos and gambling (and other activities which go along with that). Most people are happy to leave it behind after finding a bus or taxi onward.
Sisophon is tiny, and while you could probably find lodging there in a bind, doesn't seem too interesting.
There are plenty of places in Thailand that are nice enough to stay for a day. You'll always have access to good food and life, in general, is pretty relaxed. However, the only sight, as far as I know, that's really of interest and that's roughly between the two, is Ayutthaya. But that's so close to Bangkok, it sort of defeats your purpose.