I'm re-watching Buffy (as you do) and am thinking of how I would've coupled them up for the happily ever after.
Buffy with Riley (the whole point of Angel leaving was to make space for someone who could give her what he couldn't)
Angel with Harmony (I mulled this over for ages; I thought he belongs with Cordi, but actually he needs someone silly and light-hearted, with a bit of bloodsucking thrown in)
Cordi with Xander (her high standards push him to become a successful business owner and they have a nice life)
Willow eternally single, having become a supreme witch, she's outgrown human notions of love and neediness. Or maybe Oz returns and he's very wolfy and they have a new kind of relationship
Wesley with Illyria
Not sure what to do with Gunn, possibly a newly invented childhood sweetheart
Spike - no idea!
Giles with Buffy's mum
Faith with the principal guy she ended up with anyway
I'd also scrap the whole Buffy's little sister arch - what rubbish that was.