Format: Regional Mexican
"Regional Mexican" is a US record industry term invented to make buying and displaying music easier for non-Hispanic retailers. The idea behind the name is valid.  "Mexican music" is roughly equivalent to country in the US, but the genre is made up of styles that come from the different areas or regions of Mexico.
Banda comes from the northern Pacific Coast state of Sinaloa. Norteña comes from the state of Nuevo León and the area around it. Ranchera comes from the Jalisco zone. Some of the minor styles, like "durangüense" actually name the state or zone they come from. See the Wikipedia links for detailed articles about the different genres of regional Mexican.
In Mexico, the radio format consisting of any mix of these elements is called "grupera" or simply, "group music."
Some of the Principal Regional Mexican
stations in the US
Market Station Market Station Market Station
Los Angeles KBUE-FM Las Vegas KISF-FM Denver KXPK-FM
Los Angeles KDLD-FM Austin KLJA-FM Denver KBNO-AM
Los Angeles KLAX-FM Austin KLZT-FM Portland, OR KRYP-FM
Los Angeles KSCA-FM Austin KLQB-FM Houston KLTN-FM
Los Angeles KWIZ-FM Dallas KNOR-FM Riverside KRQB-FM
Chicago WOJO-FM Dallas KLNO-FM Riverside KXSB-FM
Chicago WLEY-FM San Francisco KSOL-FM McAllen KGBT-FM
San F'cisco KRZZ-FM Chicago WNUA-FM Tucson KCMT-FM
Dallas KBOC-FM Fresno KLBN-FM San Antonio KROM-FM
Houston KLTN-FM Fresno KOND-FM Atlanta WBZY-FM
Houston KTJM-FM Phoenix KLNZ-FM San Diego KLNV-FM
Houston KQBU-FM Phoenix KHOT-FM San Diego XHTY-FM
Nassau-Suffolk WQBU-FM Palm Springs, KUNA-FM    
Regional Mexican Genres
This is not a currnet "hit parade" and songs are selected to demonstrate style, not to show what is currently popular
Articles on genres of
Mexican Music
Norteña Banda Ranchera Durangüense Corrido
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Banda This style is based on large brass bands with the tuba being featured predominantly.
Banda el Recodo (l)

Arrolladora Banda
El Limon (r)
Banda MS - Increíble
El Potro de Sinaloa - El enemgo público
La Arrolladora - Niña de mi corazón
Los Rieleros del Norte - Ni el Diablo te va a querer
Montéz de Durango - Mi necesidad
Roberto Tapia - Me duele
Sergio Vega - Millonario de Amor
Saúl "El Jaguar" - Quién te dio permiso
Cuisillos - Mil Heridas
Voz de Mando - Miente en blanco
Patrulla 81 - Como pude enamorarme de ti
Banda El Recodo - Díme que me quieres
Tierra Cali - En cambio tu*
Espinoza Paz - Al diablo con lo nuestro
Banda los Recoditos - La escuelita
Julión Alvarez - Ni lo
Ranchera Ranchera and mariachi date back to the 19th Century. The music can be festive or romantic, and the orchestrations have not varied over the past 50 years.
of the

Vicente Fernández - Por tu maldito amor
Vicente Fernández - Volver, volver
Vicente Fernández - Miedo
Norteña A variable mix of pop, dance, Latin house and hip-hop, rock, reggaetón, ballads and other contemporary music types. The overlap with Adult Contemporary is considerable; A/C stations tend to play more oldies and less rhythmic songs.
Larry Hernández - Arrastrando las Patas
Chalino Sánchez - La nieves de enero
Carlos y José - El chubasco
Cardenales de Nuevo León - Se renta
Conjunto Primavera - Ave Cautiva
Los Tiranos del Norte - Hasta la miel amarga
Pesado - Ojalá que te mueras
Ramón Ayala - Tragos Amargos
Los Tigres del Norte - La mesa del rincón
Los Tigres del Norte - La jaula de oro
Mariachi Mariachi is not as much a style as a lifestyle. Ranchera artists sing to the accompaniment of a mariachi. There is no "mariachi" format, although the sound of the Mariachi is the most internationally recognized of the Mexican styles.

You will seldom hear pure mariachi music on the radio, but you will hear many songs with a mariachi backing the singer.
  Mariachi Vargas de Tecalitlán - Camino Real de Colima
Mariachi Vargas de Tecalitlán - La Adelita
Mariachi Vargas de Tecalitlán - El Carretero
Mariachi Vargas de Tecalitlán - Las Chapanecas
In Regional Mexican music, there should be a saying that "you can't keep a good song down." Many of the most famous songs get recorded again every ten years or so, or are recreated in a different genre. Here are two examples of famous songs done in different styles and in different eras.

These examples show the wide range of styles within Regional Mexican music, as well as the consistency over years and years of the basic elements. 
Versions by:
Los Alteños
Lila Downes
Juan Valentín
Instituto Mexicano del Sonido
Chalino Sánchez
Banda El Recodo
Antonio Aguilar (Karaoke track)
Antonio Aguilar
Versions by:
Ramón Ayala
Pepe Aguilar y Banda El Recodo
Patrulla 81
Mariachi Aguila
Fabiola (La Academia, Mexico's "Idol" style show)
Banda Jerez
Antonio Aguilar
Corridos Corridos are "story songs" that date to the Mexican revolution of the early 20th Century. The songs told the stories of heroes and battles and politics during the nearly 10 years of civil war in Mexico, and were the news source for the largely illiterate and rural population.

Today, corridos tell stories, too. Some are about love and life and immigration, others about the drug trade and the larger than life kingpins of drug trafficing. Playing the drug corridos is not permitted in Mexico, and in the US many major Spanish language broadcasters forbid them also. Still, those songs tell stories that reflect reality and are a part of the Music of Mexico.

Corridos may be done in a variety of styles, including norteña, ranchera and even banda-flavored ones. The distinctive element is the narrative nature of the lyrics.