Try the examples listed here

These are not for architecture jobs, but some of the lessons about emphasis and information-conveyance are still helpful.

This should give you a clue of how to approach and application process with a cover letter. Good luck!

thanks citizen, thanks poop876

Instead of Dear Mr./Ms./Dr. LastName,
how i have to start the letter if i speak to a firm? (for example SOM)

"To Whom It May Concern:" is the informal and formal salutation you can be using unless you know the person X that you are addressing it to! You can always try to call and see who the person in HR is that is responsible for hiring, or the hiring manager for the firm you should be sending your letters to.

since you mentioned SOM. Rememer that SOM laid off many of their employees, so they have to be careful if they are hiring somebody else before they hire back any of the laid off people, because if somebody finds out they could potentially be filing a law suit against the company. The only reason I'm telling you this is because SOM laid off a lot of people and they will not be hiring new staff any time soon.

"To the Human Resources Department:"

"To the Hiring Manager:"

Dear Sir or Madam....?

Okay,
first of all starting with Dear Sir or Madam, you have to know if it is a female or male. You don't want to make that mistake. Some firms don't have "hiring managers" or an HR department and addressing a company like that could make them think that you don't know much about the company and did not do enough research! I would be careful with that. You never know who is getting the letters, you never know who is reviewing resumes, so addressing it properly is very crucial.

thanks everybody,
poop876: SOM is just an example, i'm not interestested to that firm.
If a studio have a generic contact like job@... or employment@... what is the better form?

"To Whom It May Concern:" like I said is the most common used! Best of luck!

Hi there,

I would like to suggest a very nice site I found when I was looking for a cover letter some time ago.
It has a variety of cover letter examples to choose from along with cover letter writing tips. Hope you will find the best for yourself.

Poop,

Good research might reveal the sex of the recipient, but in my experience, getting beyond the receptionist can be extraordinarily difficult.
As my lawyer sister says, discovery ain't always easy.

I just recently read on monster.com that "to whom it may concern" is a turn off.

I always try to find the name of the person hiring, a department head or just address the letter to the actual company.

But don't listen to me, I haven't gotten an interview in a year. (Well that's not true, I did get about 12 responses from 50 completely fake resumes I sent out... like I listed being the Dauphin of France as experience).

<anecdotal evidence>My interview whiz friend (has gotten 8 this month) just uses "Hello!" as the greeting.</anecdotal evidence>

At the most recent first I worked for, we didn't have a hiring manager, an HR department. All incoming resumes/applications were received by the receptionists then turned over to the office manager. Office manager had instructions from the partners to sort it out based on key words and that is how they got to the desk of certain directors at the firm. This firm had couple of directors which together with the partners sorted through the resumes already sorted by the office manager, and they would make the decisions who they would want to see. If somebody sent me a resume, I would personally turn it in to the office manager and put the resumes on top of the stack or give it to the directors with my recommendation.

With that process, how the heck would you ever know who to address? So I totally agree with you Justin. There has to be a general "name" you are addressing it to.

Orchi,
remember monster deals with a lot of applications for a lot of different industries, corporate businesses etc. They may not know that much about small architecture firms and their hiring process.