Currently Fonic SIMs come with € 10 of initial credit (insted of normally € 6.75) while the SIM costs € 10, so it's virtually free and you can have a bonus of € 5 from their referral programme if you fill in another Fonic customer's number in the "Mobilfunknummer/Aktionscode" field of the online activation form, allthough it may take a couple of days until this bonus has been credited.
Except for this there's no prepaid deal (at least none relevant for data) listed at
Hauptseite ? Prepaid-wiki (under the "Aktuelle Sonderaktionen" section on the front page). Fonic would also give you cheap calls home at € 0.09/min (fixed lines) and € 0.29/min (mobiles) and it does never expire!