Ah, Illyria. What more can one say about the Big Blue Meanie? Love or hate, the only thing that matters is that you must worship.
Before the five, here's an old link I can't currently verify or find any other copies of:
"Shards of Night" by eleusis_walks (Angel, R, spoilers through 5x17 "Underneath"). Ends up in a femslashy place, but before that manages to thrill and creepify with a masterful walk through the dreams of what it means to be Illyria, and to have been Fred. First Angel fic ever for this author, so they claim, I can only pray it's far from the last.
Now for the five I could still find:
"Shell Games" by
mabus101. Xander/Illyria, set in Mabus' "Deadwar" universe. Funny, creepy, awkward, and a little bit sexy.
"Lost In the Supermarket" by Lint. Wesley takes Illyria shopping. Humor and disturbing in equal measure, in spades.
"How Tantor and Tarzan Became Friends" by
nwhepcat. Xander/Illyria. Meeting a god-king in Home Depot is just the beginning. Set in Hep's shared universe, but stands alone well on its own.
"The Sky Has Claws" by Kyra Cullinan. Fred, Illyria, Willow and Wesley explore each other body and soul. AU from "A Hole In the World". Vaguely post-apocalyptic.
Last and funniest:
"A Memorandum From Illyria" by
Hello Spikey. In the bowels of Wolfram and Hart, Illyria discovers a newer and more effective way to make her desires known.
Finally a bonus link from myself,
Faith the Vampire Slayer 1x06: "The Day After". Faith and Willow explore Los Angeles, looking for clues to the fate of Team Angel. Illyria only makes an appearance at the end, but I think it's a wonderful scene, and makes me regret all over again that I didn't continue this series.