There will never be just one Highlander crossover.
So I was just surfing on archiveofourown.org for Darcy Lewis Avenger fic I found tigriswolf fic A Taste of Lightning. It's a AU crossover with Highlander & The Avengers. It's got me in the mood of reading more Highlander crossovers especially with Methos. So basically all of tigriswolf HL fic.