Hi, I can't figure out what sounds best in some cases:

1. All you need is/are two speakers for your PC.
2. What I want is/are a few good grammar books.
3. The things I need is/are some beer and some water.
4. The things I need is/are a new PC and a new car.

Thank you in advance. 

Kooyeen wrote:

Hi, I can't figure out what sounds best in some cases: All you need is two speakers for your PC. What I want is a few good grammar books. The things I need are some beer and some water. The things I need are a new PC and a new car. Thank you in advance.

• All requires is whatever the object is (except all the girls, all the boys... are)
• What I want requires is.
• The things requires are.

He has two books cannot be He have two books and that is the point in all your examples.

However confusing it may look, the verb always matches the subject, and never the object. Only neutral expressions match the object like:

• There are several people.
• There is a book.

Kooyeen wrote:

Hi, can I disagree? From Google: By Lili Ladaga CNN Interactive Writer (CNN) -- "If you were marooned on a desert island, what would you need to survive? A Swiss Army knife? Toilet paper? Moisturizer? According to Australian writer Anna Johnson, all you need are three black skirts." This is from NPR, "Talk of the nation", May 1 2006: "What you have are these two extremes fighting each other" And this come from the Longman Dictionary: "All you need is a hammer and some nails." In the end I think it's all about tense agreement, as always (that is, I think this question has something in common with the "There is/are a cat and a dog" question). I'll post my guesses: Two speakers are all you need ---------> All you need are two speakers. A few grammar books are what I want ------> What I want are a few grammar books. Some beer and some water are the things I need ------> The things I need are some beer and some water. A new PC and a new car are the things I need --------> The things I need are a new PC and a new car.  Notice that in the sentences 3 and 4 I think "things" require "are" even though a singular noun follows.  Extra example:  A hammer and a screwdriver are all you need ---> All you need is a hammer and a screwdriver. So, those were my guesses, let's wait to see if I guessed right.

Well are/is in the cases you mentioned are the questions of style as well. But, you will not make a mistake if you take what I said and take it literally as long as you do not become a CNN journalist, or a famous writer. Then you can create rules of your own and feel when you can beat the strict grammar.

If you were marooned on a desert island, what would you need to survive? A Swiss Army knife? Toilet paper? Moisturizer? According to Australian writer Anna Johnson, all you need are three black skirts.

are is here because the journalist has mentioned one list of things already A Swiss Army knife? Toilet paper? Moisturizer? So in this case all you need  = the things you need

This is from NPR, "Talk of the nation", May 1 2006: "What you have are these two extremes fighting each other"

are is used here because "What you have is these two extremes fighting each other" would hurt ears, "is these" sounds more strange to "are these"

All you need is a hammer and some nails.

Here, is a is correct and there was none reason of style to change anything.

All you need are a hammer and some nails.

would sound worse because of "are a", so not only that is a is correct, it sounds better.

But all as a subject on its own, not a replacement for something else, requires is

All I need is several books = All [I need] is several books = All is several books

All I need is several books = [All] I need [is] several books = I need several books

All = everything what (unless you managed to give it a different meaning in the rest part of the writing)

Everything what I need is several books

However

I tried these cakes. All I tried are good. All = All cakes = The cakes

You cannot compare

Two speakers are all you need ---------> All you need are two speakers.

that is the cause of the error.

Two speakers are all you need = Two speakers are {the complete list of things that you need}.

All you need is two speakers. = All you need is {having two speakers}.

Kooyeen wrote:

Hi, I can't figure out what sounds best in some cases: All you need is/are two speakers for your PC. What I want is/are a few good grammar books. The things I need is/are some beer and some water. The things I need is/are a new PC and a new car. Thank you in advance.

Ok guys, thread resolved:

From BBC Learning English Service --- http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv149.shtml

And from "The Columbia Guide to Standard American English" --- http://www.bartleby.com/68/45/245.html

What I need is names and addresses and What I need are names and addresses are both Standard, although the notional attraction from the plural predicate nominatives will tend to make the plural are the choice.

I could have searched for this stuff before posting, I'm sorry. Anyway I want to thank you all for having expressed your opinions.