Information Resources (Score 2, Interesting)

Coverage:
http://www.t-mobile.de/funkversorgung/inland/
http://netmap.vodafone.de/cover4internet/index.jsp?appprofile=UMTS-Maps
http://www.o2online.de/nw/support/mobilfunk/netz/index.html
http://eis03sn1.eplus-online.de/evportal/portal/umts

Speed:
T-Mobile, Vodaphone have HSDPA 7.2Gb/s, O2 has HSDPA 3.6Gb/s, Eplus has 384Mb/s (UMTS)

Price:
http://www.teltarif.de/mobilfunk/datenrechner.html

As you are only interested in Prepaid, use this link and change the amount of Mb per month at the end of the URL from 310 to what you need:
http://www.teltarif.de/db/res-mobildaten.html?prepaid=1&von=Heimatnetz&mb=310

Can you read German? If so, look here:
http://www.teltarif.de/mobilfunk/

For news like this:
http://www.teltarif.de/tchibo-surfstick-30-euro/news/37951.html