Through my time with Japanese I've seen some weird words, often coming from English, mutilated by the limitations of katakana. Some are pretty obvious where they come from, but others can be tricky... Here are a couple I've noted down so far (in no particular order):
スチ／スチュワーデス: スチ being the short form, this word comes from "stewardess".
リモコン／リモートコントロール: Another word that has a shortened form, this is similar to パソコン. Comes from "remote control".
トラベル: In this word it's a combination of the last two that threw me off at first. This actually comes from the word "travel", with 'b' and the Japanese 'r'/'l'-sound substituting 'v' and 'l'.
イベント: Comes from "event".
ベートーベン: This was a headscratcher for me, as when you transliterate it it becomes beetooben; not very similar to the original name "Beethoven".
アナ／アナウンサー: This was also tricky because the first time I saw it it was in the short form. Just アナ sounds like a name, and I originally thought it was that, but then I saw it attributed to many different people. After a while I saw it in a context that also mentioned the full form アナウンサー and it was clear that it came from "announcer".
ヘルスケア: "Healthcare". There is also ヘアケア, "haircare".
キャラ／キャラクタ: "Character". I should clarify that it seems to be used only for describing the physical character, not having character as in "moral or ethical strength".
サムネイル: This I wouldn't have had the foggiest what it was unless it was in a context with many small images... "Thumbnail", as in a thumbnail-image.
サントラ／サウンドトラック: The longer form should make it clear that it comes from "soundtrack".
メアド／メールアドレス: This I saw in the Densha Otoko drama. The short version of this is particularly tricky since it doesn't really hint at what the full word could be ("mail-address").
セクハラ - I don't know if this has a long version or not, but be sure not to get into "sexual harassment".
レス: I'm not sure of this, having not confirmed it's meaning, but I've seen it in the BBS context, so I assume it would come from "response"/"respond".
スレ／スレッド: A bit of a weird one. Comes from "thread", with 's' replacing the English 'th'-sound. Tricky.
Maybe a part 2 will follow if I come across more interesting words.