 If you liked
xxxHOLiC
|
 ...then you might like
Ookami to Koushinryou
|
If you like Holo's character you will most likely like Yuko and vice versa.
Both shows showcase unique and compelling relationships, great characters, great dialogue, and complex themes. xxxHolic takes a generally darker tone, is more modern, and more fantastical than Spice and Wolf. Spice and Wolf more obviously positive. Both shows fill a similar place and if you like one, chances are you will like the other. Just keep in mind that both are unique.