Gardevoir and Granbull
You know how the song goes: "Tale as old as time. True as it can be." Gardevoir and Granbull are the Pokemon equivalent of Beauty and the Beast. The former is an elegant Psychic Pokemon that looks like it's wearing a long, flowing, and beautiful dress. The latter is a crude looking bulldog Pokemon with a seriously nasty underbite (like Bruce Springsteen's). Despite their physical differences, there's definitely love here. No matter how ridiculous they look together and no matter how many stares they get on the street, Gardevoir and Granbull show that love is much deeper than surface appearances.
Above: Gardevoir = Belle
Magmar and Jynx
The Romeo and Juliet of the Pokemon world, these two Pokemon come from warring families. Their elders simply despise each other. They go together as well as oil and water, Britney Spears and sanity, and.. well, fire and ice. While their families have been going at it for centuries, these two have manages to find love in the unlikeliest of places. Jynx is an Ice Pokemon with some serious cleavage. Magmar is a Fire Pokemon with a butt on its head. Although they've managed to find love at a time of war, their love is destined to end tragically.
Above: One half of a very fugly couple
Froslass and Rotom
These two Pokemon show that love is eternal. While their corporeal bodies may have left the Earth, their love remains. In life, this Ice and Electric Pokemon shared a legendary love. Now they are ghosts, but their feelings are unchanged. It really can last forever.