I signed up for a bunch of different wallets because I didn't know which one was the best. I have 2.5 bit coins in a wallet that I don't know how to get. I know my wallet address, but can't remember which site it's from. Can someone help me, please?
It isn't trivial to de-anonymize a bitcoin address. Your best hope is that the address has inputs or outputs to other addresses that have been deanonymized somehow (search online for those addresses). This is unlikely though. You would be better just checking all the wallet sites with your login(s). As @nate-eldredge mentions this carry's the risk that you might reveal your login/pass combinations at some exchanges that are not trustworthy.
One tool that seems to have some information about addresses is OXT. For example it determind this address to be associated with btc-e exchange