You can try the following (unfortunately I can't post links due to the rules of this site but if you google the names you should get the results up):-
The Writing on the Wall by HollyAt Elysian Fields
Summary: There was no body to bury. There was no funeral. There was nothing but the three rules and the knowledge that a thousand years of torment was nothing compared to a world without her in it. Spike embarks on a journey through the Gates of Hell to rescue the one he loves, but in order to save her, he must risk losing himself.
Chosen After Death by JackofSpikesAt Elysian Fields
Summary: Follows canon up until the Frat party with Parker then goes AU. The essence of the Power that was used to create the First Slayer has rested within Buffy since her first death at the hands of the Master - It's about to make itself known.
Consequences by Forever MeAt Sinister Attraction
Summary: That's the thing about magic. There's always consequences. Set a year after the finale, Dawn is convinced that she knows what the consequences of Willows spell are and it doesn't look good.
So That's What This Is by dampersandspoonsAt Elysian Fields
Summary: A redesigned season 6 of Buffy. What if she realized that coming back from heaven was more of a blessing than a curse? And what if Spike held the secrets to her happiness?
The Immortal Guardian Series by maryperkAt Elysian Fields
Comprises of 6 stories that involve Buffy becoming immortal (note 3 are unfinished but the others are finished).
Hope you enjoy them!!
Sarah