caolan: i studied linguistics for a few years, and as far as i know, there are no languages that are conventionally written from bottom to top.

in addition to the left-right, right-left, and top-bottom writing conventions that you mention, the only other conventional style that i'm familiar with is called boustrophedon (Greek for "turning like oxen in plowing"), which is writing that reverses direction each line.

after an initial period of being right-left about 2500 years ago, Greek was typically written in the boustrophedon style for a while before finally settling on left-right around 500 BCE. inscriptions in this style have also been found in Semitic languages, Etruscan, Latin, Ethiopian (Ge'ez), and Runic (Futhark), among others. apparently, it was a rather popular and widely failed experiment.

now that i think about it, even English is conventionally written bottom to top sometimes. the situation i'm thinking of in particular is traffic instructions in the road bed, where from above, the text is written from bottom to top (at least everywhere i've every travelled, which is limited), while the words appear sequentially to a moving commuter. there are doubtless other situations where bottom to to writing is the norm.