familysearch is a free site. I've used it for many years.
surnamedb.com is also a free site.
Last name: Paul
SDB Popularity ranking: 239
Recorded in over two hundred spelling forms throughout the Christian world this surname is of Roman (pre Christian) origins. The surname spellings range from examples such as Paul, Paule, and Pawle in England, Paolo and Paulo (Spain & Portugal), Pauli and Polo (Italy), Palle (Germany), Pabel (Czech) and Pal (Hungary), to all the patronymic and diminutive forms such as Paulson, Pauly, Paolozzi, Pavek, and many, many more. However spelt the name derives from the Latin word "paulus" meaning small, which became a baptismal term of endearment, as in 'small person'. It is...
Read more: http://www.surnamedb.com/Surname/Paul#ixzz56cwtg8MG
They don't have every surname, but they have about 50,000.