Interestingly Hallelujah reminds me of Faith/Wes. Although maybe not strickly Cannon.

Ask the sea for answers - Placebo - Totally Spike/Dru during becoming.

Give up this fight, there are no second chances.
This time I might.
To ask the sea for answers.
These bonds are shackle free, wrapped in lust and lunacy.
Tiny touch of jealousy, these bonds are shackle free.

Dido - See the sun, 100% Angel, Cordelia (friendship) after Buffy dies. (or if you ignore the 'she' references after Baby!Conner was kidnapped)

Do you remember telling me you found the sweetest thing of all
You said one day OF this was worth dying for
So be thankful you knew her at all
But it's no more

And you probably don't want to hear tomorrow's another day
Well I promise you you'll see the sun again
And you're asking me why pain's the only way to happiness
And I promise you you'll see the sun again

Also Vast - I don't have anything - totally B/A after she dies:
what can i buy to make the sky turn
blue again?
where can i go to feel like i'm alive again?
show me the places
where i can forget your name

---------

i've been stripped of everything
except some flesh that bleeds
and i've been robbed of everything
except a soul, except a soul
that needs
you
sweet you

One day - One Day I WILL do a vid for that song. It'll be a long time coming though.