AFAIK, if your transaction is more than 0.01 and old enough, it will be confirmed soon even without a fee.
-ranochigo
If your transaction size is smaller than 1,000 bytes, all outputs are 0.01 BTC or larger, the transaction is of high-priority (
https://en.bitcoin.it/wiki/Transaction_fees#Technical_info) and all your inputs are confirmed, the transaction should go through pretty soon even without a fee.
From my own personal experience, slightly more than half of them get included within the next 3 blocks and almost all of them get included within the next 6 blocks.
Did they change this? I thought it was 10 KB or below before. I've never had an issue even with a lot of inputs, so long as the output was high enough but I'm not sure if they were low or high priority transactions.