These are the ones in the original thread...
Blood of the Sire by BuffyMeetsSpike
Offers You Can't Refuse by sweetprincipale
A Chance in Hell by dampersandspoons
A Gem of a Soul by spuffy luvr
Centering by PennyDrdful
Black Satin Voices by Eurydice
Nothing to Fear by icemink
Getaway by cousinjean
Wicked Ways by noaluvjames (AH)
Driving to Distraction by BittenAndStaked (AH)
Running From the Inevitable by EnemyofReality
Down The Road I Go by Megan_Tam
Paved Road to Hell by Winsomeone
Falling by Kally77
Dirty Back Road by The Deadly Hook
Come And Go With Me by Sandy S
Gravity by buffyx
Yellow Was Desolate without Stripe by Chris
Hero by baby blues (AH)
Blood and Fire by Addie Logan
Tunnel Vision by spikes_heart
Bring Me To Life by sweetie (AH)
Dirty Work by facingthesun (AH)
Are We There Yet? By a Price
Bittersweet by Tygerlily
Now for some more...

I tend to think of parts of the Alone series as road trip-y
Alone series by spikeskat
Set during What's My Line and going A/U from there.NB sometimes these seem to lose pages but if you change the page number in the url to either put in or remove a zero before single pages (so 03 rather than just 3) that tends to fix it.
Snow Virgins by lizerrrbeathan (sequel
Spike by Snowlight)
Post Becoming - AU - Way up North. Buffy & Spike find mutual grief is the strange meeting place as they stem self destruction and the downward spiral spun from the disaster of Acathla. Story concludes twenty years later.If you can have a road trip by foot this kinda counts...
In Enemy Hearts by KittenOfDoomage
AU from Primeval: As Buffy faces off with Adam, the spell is performed but the demons break through. Buffy gets distracted and tries to save her friends, but fails. Spike gets her out and they battle their way out of the Initiative. Adam assembles his army and the world is doomed...or so it seems.It has been a long time since I read it but I think there is an element in this too...
Let's Get Lost by Herself
Set immediately post-season 2. Buffy's run all the way to NY, and encounters a Spike who feels he's made a bad bargain. Other Enemies by Chelle
This story picks up where 'Enemies' in Season Three ends.The Nearness of You by discord marie
Spike finds Buffy after she goes missing for 5 years. There are certain changes in her life that he finds, like the fact she has a daughter, who looks very familiar. Could Spike be the father and why has Buffy been hiding?