I'm sure there are some great stories out there that deal with Spike's soulful return to SunnyD. I am looking for a great multi-chaptered read. Bonus if there is an interesting plot. Please be generous?

(I have read Bag of Bones by Shadowlass. If you haven't, do)

madrog has "Who is Who" and the sequel "Relentless Revenge" at Elysian Fields. Holly has a series that starts with "Sang et Ivoire" at the same place. Spike comes back human in "A Good Man" by Ariana
http://archiveofourown.org/works/338252/chapters/547418
Magista has "The Letter" http://archiveofourown.org/works/783939/chapters/1478053
And my favorite! Kimi's "Voiceverse" starts with "Voices in the Dark" http://www.allaboutspike.com/fic.html?id=19.

all great recs - thanks for posting all the links - I've not read Kimi Voiceverse - I hope it's complete.

Sang et Ivoire was what came to mind first which smitty already mentioned.

There is also...

A Tale of Two Hearts by A Price
Spike returns with a soul and he and Buffy are kidnapped.

Driedel by Constance
An alternate start to Season Seven. Inspired by JustSue's 'Buyer Beware'
References to off-screen non-consensual sex. While this does come to a sort-of conclusion, it is essentially an abandoned WIP.

These two are possibly more AU than you are looking for...

Unreal Together by dawnofme sequel Soul Survivors
Spike comes back from Africa, in the Summer after season six, and finds that he's not the only one who's changed. When Faith's life is in danger, Buffy and Spike team up to save the day.

Perfect World by cousinjean
A slip of the tongue creates a whole new world of problems for Spike. Picks up about 4 months after "Grave." A/N: I know this looks like another one of those "Spike's back from Africa" fics, but it's not. This is one of those big, epic, plotty stories that has been stewing in my brain for much longer than Spike has had a soul. Although the soul added a whole new layer to the idea that made it too interesting to ignore.

I forgot "Grandpa" and "Samaritan" by Ivytree http://www.allaboutspike.com/fic.html?id=3