I've never used them myself, since I prefer home delivery
(if there is no-one home, a neighbour in the same house can
accept a delivery and the deliverer will put a note in our
mailbox saying with whom the parcel was left), but for a
while in Germany the post office has set up "package stations"
at various locations. These are lockers and one can collect
one's parcel there with the help of a code (which, one gets by
email or SMS). One can also send parcels as well.

There is even a web page in English:

http://www.dhl.de/dhl?tab=1&skin=hi&check=yes&lang=de_EN&xmlFile=53008

but check out the German version for different graphics:

http://www.dhl.de/dhl?skin=hi&check=yes&lang=de_DE&xmlFile=53008