Can be anything from any source, movies, books, comics, video games, manga, anime etc.
Pic related is mine, the dragonslayer from berserk. I like it because it's simple. It's just a big fucking sword, no fancy bells and whistles like enchantments or spells.
Second runner-up is sting from lord of the rings, I like that it glows blue when orcs are around and it can be used in the dark as a light source.
On the topic of bigass nonsense swords, I'm a big fan of Soul Edge (mostly for Soul Calibur 2 nostalgia reasons)
Always loved it too in those games, it's like William Birkin from RE 2 and the dragonslayer had a kid.