I've lost my cell phone and need to replace it w/o changing my contract. Any suggestions on where I could buy a reasonable priced handy without a contract? Does anyone have a phone they would like to sell? It would need to be either unlocked or o2 compatable. thanks.

Have you heard of ebay?

i bought mine over ebay because although i am with o2, buying it off of e-bay, from a reputable shop, saved me over 100 Euros as opposed to buying it in the O2 shop´in Mannheim.

I got mine (with contract) from Handys Mobile. But they also have unlocked phones without contract. I got my two last ones from there, as did my best friend and we did not experience any issues with them. Reviews on Ciao.de.
They have free shipping within Germany. But they only sell new phones, so if the price is a big issue for you, Ebay is probably a better suggestion. Their prices, at least for phones with a contract, are excellent, but you still pay quite a bit for a phone without a contract. Example (for a phone with contract): I paid €6 for mine with a Vodafone contract. At Vodafone, the same phone (same plan, same everything) would have cost me over €200.