It was difficult to find words that didn't emphasize or loan words. One example I found was the word キヤノン which is for Canon, the Japanese camera company. After doing some research, I found that Canon was formerly named Kwanon after Guanyin (called Kannon in Japan), a bodhisattva (confusing, I know). So basically, it ended up just being a way to write a foreign name. I don't quite understand why it's キヤノン and not カノン. Many other companies seem to use katakana for writing their names, if they don't use romaji already. It seems that wherever katakana is used for emphasis, companies tend to also just use English to further that point as seen in companies like Toyota. Many company names also use katakana but happen to be loanwords like レイク(lake) and プロミス (promise).
In manga, katakana is often used for onomatopoeia. In the Dragon Ball manga below, every kind of action is also given a sound effect. In the right page, the kamehameha is given a sound effect represented as キュアアツ. In the left page, jumping is given a sound effect represented as パツ. Truthfully, I think these representations are just as bad as the ones on American comics.
I read that katakana is also used to depict foreign accents or robotic speech in writing which seem to also fall under emphasis. Additionally, katakana (and only katakana) was used in telegraphs years ago. Scienctific terms are generally expressed in katakana.
I found a great website with unusual uses on katakana:
http://gakuranman.com/unusual-katakana-words/
*from aforementioned page
I'll pretend some terms aren't there:
バーター (sidekick) and デマ (rumor) are definitely not loanwords from English, so it could be from another language, but it could also be emphasis. If none apply, these are definitely a special cases.