All of these are very long, at least 60k+ words (mostly).
The Student Prince - quite possibly one of the most amazing fics I have ever read. My only possible complaint is that I wish it had kept going, and it's already 100k words long, so. Yeah. This is hysterical, and sweet, and full of UST for the first half and utter sweetness for the second half without ever being unpleasant or too soppy. I love it. To pieces. So go read it, now.
Tristan & Isolde - Similarly amazing, but in less of a "funny AU" sort of way and more of a "amazingly romantic and utterly legend-soaked non-AU" kind of way. It's fabulous. And romantic. Did I mention romantic? Also funny, but less uproariously and more squeeably. It's fantastic. Amazing. I am speechless, as per usual, but this time it's because this fic is is amazing.
The Knights Have a Thousand Eyes - The best portrayal of the knights of Camelot EVER, this is adorable and sweet with an interesting plot, romance, loyalty and a fantastic cast of side characters who, while original, are anything but awful.