PAYWARE:
S Bahn Rhein Main : https://www.justtrains.net/product/s-bahn-rhein-main
BR 430 : http://www.railtraction.eu/train-simulator/multiple-units/electric-multiple-units/br430-s-bahn.html
BR 420 : http://store.steampowered.com/app/222599/Train_Simulator_DB_BR420_EMU_AddOn/?l=german
BR 648 (Railtraction) : http://www.railtraction.eu/br-648.html

FREEWARE :
BR 420 S Bahn Rhein Main : http://rail-sim.de/forum/wsif/index.php/Entry/3705-STWS-ET420-S-Bahn-Rhein-Main-BETA-3-1/
BR 648 HLB :  http://rail-sim.de/forum/wsif/index.php/Entry/1354-BR-648-HLB/