I've used efilemyforms, but I think that Track1099 and TaxBandits are probably more popular.  As Rick said, if you want to send the 1099s to the recipients, you can use the fairly new IRIS from the IRS.

It partially may depend on (1) how many 1099s you need to file and (2) if your State also requires 1099s to be filed with the State.