A list of the most common Spanish surnames is available on Ancestry.com. It lists the five most common surnames as García, Fernández, González, Rodríguez and López.
Other websites, such as Family Education and Wikipedia, have a more complete list of Spanish surnames. It is rare for Spanish surnames to begin with certain letters. Only a few Spanish surnames, such as "Yanes," begin with the letter "Y." Similarly, there are a limited number of Spanish surnames that begin with the letter "U," such as "Urquía." The letters "K" and "W" are extremely rare in Spanish and are used for loanwords. Thus, Spanish surnames almost never begin with a "K" or "W."