well, since I'm in the middle of doing just that, here's some pointers:
Leave your debit card at home, the fees for using it are ASTRONOMICAL. Credit cards (VISA, Mastercard and AMEX) are your best bet, acceptable everywhere and the fees are much less.
If you can find a friend that is in the US military stationed in germany (Rammstein, Weisbaden, etc) that will be your BEST way to get money out of your account. if not, run yourself on a cash-only economy.
Keep your passport on you at ALL times.
I would suggest finding more people to travel along with, as group discounts are available on EVERYTHING and with more people, you are less likely to run into trouble.
Americans are loud obnoxious assholes, and you will realize this the moment you step foot out of the airport. Try VERY hard, NOT to be one.
LEARN SOME LOCAL LANGUAGE! although many Germans speak and understand English, they are much more willing to help you out if you can understand and speak a little German, it just shows some courtesy otherwise you're just "ananderes doof amerikaner" (another stupid american)
T-Mobile is unfortunately the way to go for international cellphone service. If you're not with a GSM carrier, you might as well leave your phone at home (if you have sprint, verizon or metropcs, your phone will be a paperweight). I would suggest picking up a prepaid "burner" phone when you get here.
If you fly into frankfurt, you are not far from Wiesbaden, and I have yet to run into too many people who can't communicate in english there.
RailPass is awesome, just make sure you get one that covers the routes you want to take.
Whatever amount of money you have in mind to save and take along, DOUBLE IT, RIGHT NOW!
of course, the best way to do it is to get a multinational corporation to pay your arse to be there, but that's not an option for everyone.
everything you want to bring with you that you may want to plug into the wall MUST support 230v/50hz power. general rule of thumb, if it contains a directly powered A/C motor and doesn't have a rechargable battery, leave it in the states and buy one when you get here, most Laptop/PC power supplies are autoswitching, so you just need to get a "SCHUKO" power cord for it. screw the adapters, they're a pain in the arse..
ANYTHING that is chargable via USB is easy, just buy a universal charger wallwart when you get here, they're about 10 euro ($13), phones, digital cameras, bluetooth accessories are mostly usable this way.
hostels are cheap, but germans are strange, and I don't know if I'd stay in german hostels. the actual hotels have a surprising level of service. I'm currently staying at Hotel Toskana in Wiesbaden, and every morning I can eat all the eggs and bacon I want for free, all the shots from the bar are double pours and MUCH cheaper than bars/restaurants around the area.
but the biggest suggestion I can give you is BRING MONEY! money will solve more problems for you than anything else you can bring.