Surname prefixes and suffixes by ethnicity.

[Don Brick]

Finnish names often end in -nen or -la/-lä.

Yup and to further clarify things the -nen ending usually indicates Eastern Finnish origin while the other one western origin, but of course things tend to be quite mixed up nowadays, but roughly speaking.

[Electronic God-Man]

Lithuanian names often end in -as, -is or -us.

Ex. Majauskas, Macevicius, Unitas, Butkus, Norkus, Janavicius, Adomaitis, Uzugiris, Jankauskas, Naujokis, Paulauskas, Mielkus, Kulesius, Bielinis, Malinauskas, Staugaitis, Dovydaitis, Smilgevicius, Sernas, Basanavicius, Klimas, Mironas, Bizauskas, etc.

[Rouxinol]

Let me add that "de" in Portuguese names means "from" - the equivalent to "van" in Dutch and "von" in German. My last name has toponymic origina in a little village near the one my father was born in Minho (northern tip of Portugal, near Galicia). The first family to adopt this surname was that of one archbishop of Braga (also in Minho) born in the 13th century.

Examples:
- de Vasconcelos
- de Oliveira
- de Sousa
- de Carvalho
- de Assis
- de Meneses
- de Souto
(...)

[Comte Arnau]

As far as Portuguese and Spanish names go, names that end in -ez in Spanish end in -es in Portuguese (Lopez/Lopes, Marquez/Marques, etc.).

Not to confuse ethnicities with nationalities, better say that surnames ending in -ez are Castilian, not Spanish. Surnames of other ethnicities within Spain do not end in -ez.

In Catalonia, the few surnames ending in -is (Gomis, Peris, Llopis, Ferrandis...) are adaptations of the Castilian ones (Gómez, Pérez, López, Fernández...), but they are rare, only being relatively common in Valencia because of Navarro-Aragonese influence. Instead of that genitive ending, the use of the patronymic in Catalan lands was usually with a simple de, although it was also used to mean place origin. Surnames here were also more focused on professions, placenames, qualities...

Some common Catalan surnames meaning professions:

Ballester/Ballesté = Crossbow maker
Baster/Basté = Saddler
Bover/Bové = Oxherd
Escuder/Escudé = Squire
Ferrer/Ferré = Smith
Mercader/Mercadé = Merchant
Mestre = Master, Teacher
Moliner/Moliné/Munné = Miller
Oliver/Olivé = Olive trader
Oller/Ollé = Potter (Pot maker)
Pagès = Farmer
Pellicer = Furrier
Piquer/Piqué = Quarryman, Stonemason
Sabater/Sabaté = Shoemaker
Teixidor/Teixidó = Weaver

Some referring to place names:

Bosch = Wood
Fàbregues/Fàbregas = Factories
Mas = Catalan country house
Pla = Plain
Pont = Bridge
Puig = Hill
Pujol = Hillock
Riera = Stream
Rovira = Oak wood
Serra = Mountain range
Valls = Valleys
Vila = Town

Some related to qualities:

Amorós = Lovely
Anglès = English
Antich = Ancient
Bonet = Kindhearted
Fort = Strong
Llord = Dirty, ugly
Roig = Red
Ros = Blond
Rossell = Little blond

Some common surnames which come from names

Andreu = Andrew
Dalmau = Dalmatius
Domènech = Dominicus
Grau < Guerau =Gerald
March = Mark
Mateu = Matthew
Martí = Martin
Mir = Mirus
Sans/Sanç/Sanz = Sanctius

[Treffie]

Is there any truth to the idea that the Mc- prefix is Irish and Mac- is Scottish? Or do you find both in both places?

Mc or Mac can be both Scottish and Irish. The Welsh equivalent is ap/ab which has its origins from Mab. All three mean `son of`.

[leisitox]

Italian names often end in cci-ni like Cecconi, Musolini and Ricci for example.
Sweden names end in berg-son/sson-sen/ssen-ström/strøm for example Winberg, Svenson,Walfridsson, Andresen, Hanssen, Hallestrøm,Hegstrom for example

[Ibericus]

As far as Portuguese and Spanish names go, names that end in -ez in Spanish end in -es in Portuguese (Lopez/Lopes, Marquez/Marques, etc.).
?

The suffixes -ez, -az,(as in Fernández or Díaz) are of germanic origin and means 'son of '

[askra]

typical sardinian surnames end with -s or -u

common suffixes are:

• as/is/us Cann-as, Pir-as, Marr-as, Solin-as, Ros-as, Vird-is, Lamp-is, Camp-us, Ang-us, Pint-us
  
• au Bidd-au, Mad-au, R-au
  
• edda Del-edda, L-edda, Z-edda, Fa-edda
  
• u Al-u, Sor-u, Pa-u, Ra-u, Niedd-u, Ar-u, Ruj-u

[Comte Arnau]

The suffixes -ez, -az,(as in Fernández or Díaz) are of germanic origin and means 'son of '

Yes, a mark of the Germanic genitive. Also used for names from other origins.

PÉREZ Son of Pero (Peter) = Peterson, Parkinson, Pierson, Peters, Pierce ...
MÁRQUEZ Son of Marco (Mark) = Markson, Marks
GONZÁLEZ Son of Gonzalo (Gundisalvus)
FERNÁNDEZ, HERNÁNDEZ Son of Fernando (Ferdinand)
LÓPEZ Son of Lope (Wolf)
RODRÍGUEZ Son of Rodrigo (Roderick)
MARTÍNEZ Son of Martín (Martin) = Martinson, Martins
SÁNCHEZ, SÁENZ, SÁEZ Son of Sancho (Sanctius)
GÓMEZ Son of Gomo, short for Gomesano (Gumesandus)
JIMÉNEZ, GIMÉNEZ Son of Jimeno (prob. Simon) = Simonson, Simons, Simmins
RUIZ Son of Ruy, short for Rodrigo.
DÍAZ, DÍEZ, DÍEGUEZ Son of Día/Diego (Didacus, James, Jacob) = Jameson
ÁLVAREZ = Son of Álvaro (Alvarus)
GUTIÉRREZ = Son of Gutier or Gutierre (Gunther)
NÚÑEZ Son of Nuño (Nonnus)
DOMÍNGUEZ Son of Domingo (Dominicus)
VÁZQUEZ, VELÁZQUEZ, BLÁZQUEZ Son of Velasco (Basque name Belasko, little raven)
RAMIREZ Son of Ramiro (Ramirus) = Reymers in Germanic
SUÁREZ, JUÁREZ Son of Suero (Suarius)
MÉNDEZ, MENÉNDEZ, MELÉNDEZ Son of Mendo (Hermenegild)
MUÑOZ, MUÑIZ Son of Muño (Munnius)
IBÁÑEZ Son of Ibaño, Ibán, Juan (Ivan, John) = Johnson
BENÍTEZ Son of Benito (Bennet, Benedict)
PÁEZ, PELÁEZ Son of Payo, Pelayo (Pelagius)
BERMÚDEZ Son of Bermudo (Bermudus)
ANTÚNEZ Son of Antonio, Antón (Anthony)
ORDÓÑEZ Son of Ordoño (Ordonius)
etc...

[Bloodeagle]

Another suffix associated with a distinct type of English folk name is ing or ings.

The Old English ending ingas means "the descendants, followers or people of", represented by such names as Avening, Epping, Eddings, Hastings, and Reading.