L is a brilliant, reclusive young detective and Misa is a spunky pop idol. But despite being so glaringly different, the two of them are (in my opinion) the most interesting characters in Deathnote. And while you can join this fanlisting if you appreciate any aspect of their relationship (be it friendship, rivalry, etc.), I personally think they would make a cute romantic pair.
Why? It probably boils down to the fact that L is my favorite character, and I always have the urge to pair my favorite character with someone. Misa happens to be one of the very few recurring female characters in Deathnote, and I also happen to adore her. So it's a no-brainer for me to stick them together. And then there's the fact that I think Misa is entirely too good for Raito/Light, but that's another story.
But beyond my personal interests, I think the two of them could potentially work well together. L could use someone like Misa to help him improve his social life. He had admitted openly that Raito was his first friend, and Misa was his second (that's... pathetically sad). The guy seriously needs to get out more. Misa could drag him out of his shell. And on the other side, Misa could use a stable boyfriend who would appreciate her (L compliments Misa many, MANY, times more than Raito ever did).
There is also a tiny bit of evidence in the actual manga, which includes the small kiss Misa gave L (see image above). It was a friendly kiss, of course, but I'm free to view it as more than that if I want. XD When L first meets Misa, he tells Raito that he envies him (obviously, he envies the fact that Raito has such a cute girlfriend). L also says that he's a fan of Misa, though it's debatable whether or not he was telling the truth or simply letting Raito know that he was knowledgeable about her. Later, there is the kiss, and L says something about falling love with her, to which she responds "We can be friends" (or something to that effect). There is then a cute moment of L, Misa, and Raito holding hands and sort of... dancing in a circle? Also of interest is the fact that Misa has a tendency to grab L's hair when she gets annoyed with him, and he doesn't seem the least bit bothered by it. :D
!!! Huge Spoilers !!!
Yes, I am fully aware that L is dead and that he and Misa will never be a pair. But honestly, I know they'd never be a pair even if he never died, so what's the point of changing my views now? That, and I still have that L-is-still-alive theory. XD