When to use the verb "Ser" and when to use "Estar"
 

A quick comparison between Ser and Estar
Disclaimer: This is basically off the top of my head so some things could be missing. If you see something that should be here and it's not, please post it. In any case, it's a good start for learning when to use ser and when to use estar.

Ser is used for:

• Professions - Soy carpintero - I'm a carpenter
  
• Permanent conditions - La ciudad es muy sucia - The city is really dirty (A fact of life, unlikely to change)
• Permanent characteristics - Soy bajita - I'm short; El martillo es pesado - The hammer is heavy
• Definitive characteristics even if they're not permanent - El es nuevo aquí. - He's new around here.
• Where someone is from - Soy de España - I'm from Spain
• Telling time - Son las 3 de la tarde - It's 3 PM
• Saying what the date is - Es el tres de octubre - It's October 3rd
• Saying what day of the week it is - Es lunes - It's Monday
• Nationalities - Ella es francesa - She's French
• Possesion - La cámara es de Miguel - The camera is Michael's
• What something is made of - La pared es de ladrillo - The wall is made of/from brick
• Religion - Es católica - She's Catholic
• Size & Length - El palo es largo - The stick is long; El bolígrafo es pequño - the pen is small
• Colors - Las rosas son rojas - Roses are red
• To specify one of several object don't confuse this with the location criteria below - ¿Cuál es la casa de Juan? Es la casa de la esquina. - Which house is Juan's? It's the house on the corner.

Estar is used for:

• Changeable conditions - La calle está sucia - The street's really dirty (It just rained and there's mud everywhere, not a permanent condition)
• Changeable characteristics - Está enojado - He's angry
• Location/position of people/things Even if it's something permanent - Está en la recámara - It's in the bedroom; Londres está en Inglaterra - London is in England
• Temporary state of something - La luz está prendida - The light is on; La puerta está abierta - The door's open
• Used to form the "-ing" form of verbs - Estoy caminando - I'm walking

You can use either ser or estar for certain things, both are correct, but have different meanings:
There are many more examples of this. As I think of them, I'll try to add them.

Juan es aburrido - Juan is boring
Juan está aburrido - Juan is bored

María es nerviosa - Mary is a nervous person
María está nerviosa - Mary is nervous (right now, but not always)

El mango es bueno - Mangoes are good
El mango está bueno - This mango tastes good or The mango is good (as in not rotten or spoiled)

Es buena - She's a good person
Está buena - She's hot

Re: When to use the verb "Ser" and when to use "Estar"
 

This is a great tutorial, it cleared up alot of things for me. Thanks. ;D

Re: When to use the verb "Ser" and when to use "Estar"
 

Good one Tomisimo. It helped me a lot.

Re: When to use the verb "Ser" and when to use "Estar"
 

Glad to help guys :)

David, you wrote carpinter, instead of carpenter. I know it's a typo, but...

That's very helpful, David (says he whilst taking a screen shot).

I fixed the typo and I'm glad it's useful :)

Ser y Estar
 

It really helped me to see the sentences where ser and estar were switched.
Estar can be 'what is now', and, Ser can be 'what it is in itself', no?

-Chris

I think that's a helpful way to think about it, yes. :)

También:

SER: Tener lugar (take place).
p.e ?Dónde será la boda de Alberto?