Italian Surname Database

According to an article in http://italian.about.com/od/italianculture/a/aa111704a.htm, written by Michael San Filippo, the top 20 surnames in Italy appear below. I have also included the meaning for each as well as alternate spellings. Russo and Rossi seem to be the most common.
ROSSI – A red-haired or ruddy-complexioned individual, derived from the nickname “rosso,” meaning ‘ red.’ Most common in northern Italy. Surname Origin: Italian

Alternate Surname Spellings: ROSSO, ROSSA, RUSSI, RUSSO, RUGGIU, RUBIU, ROSSELLI, ROSSELLO, ROSSELLINI, RISSIELLO, ROSSILLO, ROSSETTI, ROSSETTO, ROSSETTINI, ROSSITTI, ROSSITTO, ROSSINI, ROSSINO, ROSSOTTI, ROSSOTTO, ROSSINI, ROSSONE, ROSSUTO, RUSSELLO, RUSSINO, RUSSOTTI, RUSSOTTO, RUSSIANI, RUSSOLILLO
RUSSO – This southern Italian variation of the ROSSI surname which means “red-haired or ruddy-complexioned individual.” Derived from the nickname “rosso,” meaning ‘ red.’ Surname Origin: Italian

Alternate Surname Spellings: ROSSI, RUSSELLO, RUSSINO, RUSSOTTI, RUSSOTTO, RUSSIANI, RUSSOLILLO
FERRARI- An occupational surname from the Italian word “ferraro,” meaning ‘blacksmith” – originally derived from the Latin ferrum meaning “iron.” The Italian equivalent of the surname SMITH. Surname Origin: Italian

Alternate Surname Spellings: FERARI,
ESPOSITO – A last name commonly given to children in Italy (prior to its unification in 1861) who were abandoned or given up for adoption by their parents. From the Latin “expositus,” the past participle of the Latin verb “exponere,” which means ‘to place outside.’ Especially prevalent in the Naples region of Italy. Surname Origin: Italian

Alternate Surname Spellings: ESPOSTI, ESPOSTO, ESPOSTI, DEGLI ESPOSTI,
BIANCHI – From “bianco,” meaning ‘white,’ this surname was often given to a person who was white-haired or had a very light complexion. Surname Origin: Italian

Alternate Surname Spellings: BIANCA, BIANCO, BIANCHESSI, BIANCHETTI, BIANCHINI, BIANCIOTTI, BIANCOLINI, BIANCONCINI, BIANCOTTO
ROMANO – The Italian form of “Romanus,” the Latin word for ‘Rome,’ this popular Italian surname was often used to denote someone from Rome, Italy. Surname Origin: Italian

Alternate Surname Spellings: ROMANI
COLOMBO – From the word “colombo,” meaning ‘dove,’ Colombo was a name often given to a dove keeper. Surname Origin: Italian

Alternate Surname Spellings: COLOMBANI, COLOMBERA, COLOMBINI, COLOMBRINO
RICCI – Derived from the Italian adjective” ricco,” meaning ‘curly,’ RICCI and its variations are a nickname for someone with curly hair. Surname Origin: Italian

Alternate Surname Spellings: RICCIO, RIZZI, RIZZO, RIZZA, RISSO, RICCELLI, RICCIARELLI, RICCETTI, RICCINI, RICCIOLI, RICCIOLINO, RICCIULLI, RICCIOTTI, RICCIONI, RICCIUTO, RICCERI, RICCITIELLO, RIZZELLO, RIZZIELLO RIZZETTI, RIZZETTO, RIZZINI, RIZZOLI, RIZZOLA, RIZZOTTI, RIZZONI, RIZZONE, RIZZARI, RIZZATO, RIZZIERI, RIZZUTI, RISSOLO
MARINO – Derived from the Latin word “marinus,” meaning ‘of the sea,’ the Marino and Marini surnames indicate someone who lives or works near the ‘mare,’ or sea. Surname Origin: Italian, Spanish

Alternate Surname Spellings: MARINI, MARIN, MARINELLI, MARINELLA, MARINIELLO, MARINETTI, MARINUZZI, MARINOLLI, MARINOTTI, MARINONI, MARINATO, MARINACCI
GRECO – Someone who originates from Greece. Surname Origin: Italian

Alternate Surname Spellings: GRIECO, GRECI, GRECHI, GREGO
BRUNO – From the Italian word for “brown,” Bruno was, a nickname for a person with brown hair, skin, or clothes. From the German “brun,” meaning dark, brown. Surname Origin: Italian

Alternate Surname Spellings: BRUNI, BRUNA, BRUNAZZI, BRUNELLO, BRUNERI, BRUNONE, BRUNORI
GALLO – From the Latin “gallus,” meaning ‘cock, rooster,’ this was a nickname for a proud person, especially one with a “cocky” or vain attitude. Surname Origin: Italian, Spanish

Alternate Surname Spellings: GALLI, GALLETTI, GALLINI, GALLONI, GALLUCCI
CONTI – From the Old French “conte”, meaning count, it denoted a person who worked for a count (noble) or was possibly himself a count. Surname Origin: Italian

Alternate Surname Spellings: CONTE, CONTIELLO
DE LUCA – A patronymic surname meaning “son of Luca.” The given name Luca is the Italian version of Luke, from the Greek name Loukas meaning “from Lucania,” a region in Italy. Surname Origin: Italian

Alternate Surname Spellings: DI LUCA, DILUCA
COSTA – Meaning “coast” or “riverbank,” this surname denoted a person who lived by a river or the sea. Surname Origin: Italian, Spanish, Portugese

Alternate Surname Spellings: DA COSTA, DI COSTA, DE COSTA
GIORDANO – The Italian form of the name Jordan, this surname has its roots in “Yarden,” the Hebrew name of the Jordan river flowing between the countries of Jordan and Israel. Derived from “yarad,” meaning ‘descend’ or ‘flow down.’ Surname Origin: Italian

Alternate Surname Spellings: GIORDANI
MANCINI – From the Italian word “manco,” meaning ‘left-handed.’ Surname Origin: Italian

Alternate Surname Spellings: MANCINO, MANCINELLI
RIZZO – A variant of the common Italian surname RICCI, which is derived from the Italian adjective” ricco,” meaning ‘curly.’ In other words, a nickname for someone with curly hair. Surname Origin: Italian

Alternate Surname Spellings: RICCI, RICCIO, RIZZI, RIZZA, RISSO, RICCELLI, RICCIARELLI, RICCETTI, RICCINI, RICCIOLI, RICCIOLINO, RICCIULLI, RICCIOTTI, RICCIONI, RICCIUTO, RICCERI, RICCITIELLO, RIZZELLO, RIZZIELLO RIZZETTI, RIZZETTO, RIZZINI, RIZZOLI, RIZZOLA, RIZZOTTI, RIZZONI, RIZZONE, RIZZARI, RIZZATO, RIZZIERI, RIZZUTI, RISSOLO
LOMBARDI – A geographical surname for someone who came from Lombardy, a region in Italy which got its name from the Lombards, a Germanic tribe who invaded in the 6th century. Surname Origin: Italian

Alternate Surname Spellings: LOMBARDO, LOMBARDINI, LOMBARDELLI
MORETTI – 1- Derived from a diminutive of the given name Mauro, the Italian form of Maurus, meaning “dark-skinned” or used to refer to someone coming from Mauritania in northern Africa. 2- Possibly derived from the word “morro” meaning ‘rock.’ Surname Origin: Italian

Alternate Surname Spellings: MORETI, MORO, MORELLI, MORINI, MORUCCI, MORUZZI, MORUCCHIO, MORATELLI, MORISI, MORATTI, MORAZZI, MORASSUTTI, MORESCHI, MORONI

Unfortunately, the article does not site sources which is disappointing.