I'm not big on baby!fics (although there are some excellent ones mentioned above), but I have a couple:
If That's What it Takes - Spike and Buffy are accidentally sent to an alternate dimension (bad Willow!) where they are normal humans and married to each other. They are there long enough to become a real couple. When Willow brings them back to Sunnydale, Buffy recoils from Spike and he leaves. Until she has to bring him back because she has a surprise for him.
A Very Bumpy Christmas (and many of the shorter schmoop bingo fics written in that verse) is a baby fic.
Set in the world of [b]Things That Go Bump in the Night[/b] it follows by several months Spike's reappearance in that fic.
Some of my AU future fics (Always Wait For You, for example) have a future Spike and Buffy with children, but they aren't baby fics.