If you go to the blockchain.info site and search for your address you will come up with a list of transactions like this:
http://blockchain.info/address/14aRpAo5KuHvKbidiPJZ7LtfwLf62ZGbJLLook on the left hand side and you can see the sender's address.
Of course you have to know the sender's address for this to be useful, but such is the anonymity of bitcoin.
If the transactions come from recently mined coins, you might be able to trace them back a couple transactions and find the mined block, which should be labelled with the mining pool or ip that found that block.
Good luck!