I don't really know what slowcore means, but all these bands have a medium to snail pace and usually a long, luxurious discography. It seems several of these bands were around 10 years ago but have been forgotten by all but a few who adore them, hough more recent suggestions welcome. Here is a larger list of what I am familiar with:

Low
The Czars
RHP (plus other Kozelek work)
Devics
Sparklehorse
The Blue Nile