The fantastic Woodlouse spider, Dysdera crocata - does exactly what it says on the tin, eats woodlice (and other inverts it comes across I'm sure). This is one of the species of spider that are synanthropic, which implies that they like to live alongside us - the reality is that they just love the shelter and habitat that we provide around the outsides of our homes and gardens. They occasionally venture inside, in my experience this often coincides with heavy rain and they are simply looking for a dry spot - poor things.
What a beautiful spider, I used to keep two when I was small. I called one of them strawberry and the other was called red! I let them go after about 2 weeks because I felt mean feeding woodlice to them!