The following stories (in no particular order) are all epic in length and predicated on the notion that Angelus and Spike have always had a bond much stronger than just ‘friends’ or even occasional bedmates and once the misunderstandings/subterfuge/self-denial are dealt with, they seem to have a difficult time keeping up the 'mutual hatred & loathing' charade.
1. Sketches by Kathleen O’brien
Buffy helps her two favourite vamps rekindle an old flame. (The last link I had to this story was at My Immortal Beloved, which seems to be now defunct, so if anyone knows of another place where it's archived, feel free to comment with a link so I can update).
2.
Two Parts of the Same by CrazyEvil Dru
Angel and Spike celebrate American holidays and their protean relationship over the course of a few years in LA.
3.
Number One Lowest Common Denominator by Adsum
Reminiscences draw a chipped Spike to Angel's doorstep.
4.
Bloodlines by P'al Kwai
Spike is poisoned and Angelus returns, but that's just the beginning of the story...
5.
The Longest Distance Between Two Points by Jenny
"Angelus makes a promise to William that changes William's life. Many years later, Angel comes to Sunnydale to remind Spike of that promise."