from:http://esl.about.com/cs/vocabulary/a/a_confused.htm

Here are some of the most commonly confused English word pairs. They have been chosen especially for ESL learners. The list is not complete, if you have any commonly confused words that you feel should be included. Send me an esl.guide@about.com.

beside / besides

beside: preposition meaning ‘next to’, ‘at the side of’

Examples:

I sit beside John in class.
Could you get me that book? It’s beside the lamp.

besides: adverb meaning ‘also’, ‘as well’; preposition meaning ‘in addition to’

Examples:

(adverb) He’s responsible for sales, and a lot more besides.
(preposition) Besides tennis, I play soccer and basketball.

clothes / cloths

clothes: something you wear – jeans, shirts, blouses, etc.

Examples:

Just a moment, let me change my clothes.
Tommy, get your clothes on!

cloths: pieces of material used for cleaning or other purposes.

Examples:

There are some cloths in the closet. Use those to clean the kitchen.
I have a few pieces of cloth that I use.

dead / died

dead: adjective meaning ‘not alive’

Examples:

Unfortunately, our dog has been dead for a few months.
Don’t touch that bird. It’s dead.

died: past tense and past participle of the verb ‘to die’

Examples:

His grandfather died two years ago.
A number of people have died in the accident.

experience / experiment

experience: noun meaning something that a person lives through, i.e. something that someone experiences. – also used as an uncountable noun meaning ‘knowledge gained by doing something’

Examples:

(first meaning)His experiences in Germany were rather depressing.
(second meaning) I’m afraid I don’t have much sales experience.

experiment: noun meaning something that you do to see the result. Often used when speaking about scientists and their studies.

Examples:

They did a number of experiments last week.
Don’t worry it’s just an experiment. I’m not going to keep my beard.

felt / fell

felt: past tense and past participle of the verb ‘to feel’

Examples:

I felt better after I had a good dinner.
He hasn’t felt this well for a long time.

fell: past tense of the verb ‘to fall’

Examples:

He fell from a tree and broke his leg.
Unfortunately, I fell down and hurt myself.

female / feminine

female: the sex of a woman or animal

Examples:

The female of the species is very aggressive.
The question ‘female or male’ means ‘are you a woman or a man’.

feminine: adjective describing a quality or type of behaviour that is considered typical for a woman

Examples:

He’s an excellent boss with a feminine intuition.
The house was decorated in a very feminine manner.

its / it’s

its: possessive determiner similar to ‘my’ or ‘your’

Examples:

Its color is red.
The dog didn’t eat all of its food.

it’s: Short form of ‘it is’ or ‘it has’

Examples:

(it is) It’s difficult to understand him.
(it has) It’s been a long time since I had a beer.

last / latest

last: adjective usually meaning ‘final’

Examples:

I took the last train to Memphis.
This is the last test of the semester!

latest: adjective meaning ‘most recent’ or ‘new’

Examples:

His latest book is excellent.
Have you seen his latest painting?

lay / lie

lay: verb meaning ‘to put down flat’ – past tense – laid, past participle – laid

Examples:

He laid his pencil down and listened to the teacher.
I usually lay my pies on the shelf to cool.

lie: verb meaning ‘to be down’ – past tense -lay (be careful!), past participle – lain

Examples:

The girl lay on the bed asleep.
At the moment, he’s lying on the bed.

lose / loose

lose: verb meaning ‘to misplace’

Examples:

I lost my watch!
Have you ever lost anything valuable?

loose: adjective meaning the opposite of ‘tight’

Examples:

Your trousers are very loose!
I need to tighten this screw. It’s loose.

male / masculine

male: the sex of a man or animal

Examples:

The male of the species is very lazy.
The question ‘female or male’ means ‘are you a woman or a man’.

masculine: adjective describing a quality or type of behaviour that is considered typical for a man

Examples:

She’s a very masculine woman.
His opinions are just too masculine for me.

price / prize

price: noun – what you pay for something.

Examples:

The price was very cheap.
What’s the price of this book?

prize: noun – an award

Examples:

He won a prize as best actor.
Have you ever won a prize in a competition?

principal / principle

principal: adjective meaning ‘the most important’

Examples:

The principal reason for my decision was the money.
What are the principal irregular verbs?

principle: a rule (usually in science but also concerning morals)

Examples:

It’s the first principle of aerodynamics.
He has very loose principles.

quite / quiet

quite: adverb of degree meaning ‘very’ or ‘rather’

Examples:

This test is quite difficult.
He was quite exhausted after the long journey.

quiet: adjective meaning the opposite of loud or noisy

Examples:

Could you please be quiet?!
She’s a very quiet girl.

sensible / sensitive

sensible: adjective meaning ‘having common sense’ i.e. ‘not stupid’

Examples:

I wish you would be more sensible about things.
I’m afraid you aren’t being very sensible.

sensitive: adjective meaning ‘to feel very deeply’ or ‘to hurt easily’

Examples:

You should be careful with David. He’s very sensitive.
Mary is a very sensitive woman.

shade / shadow

shade: protection from the sun, a dark area outside on a sunny day.

Examples:

You should sit in the shade for a while.
It’s too hot. I’m going to find some shade.

shadow: the dark area created by something else on a sunny day.

Examples:

That tree casts a large shadow.
Have you every noticed your shadow getting longer as it gets later in the day?

some time / sometimes

some time: refers to an indefinite time in the future

Examples:

Let’s meet for coffee some time.
I don’t know when I’ll do it – but I will do it some time.

sometimes: adverb of frequency meaning ‘occasionally’

Examples:

He sometimes works late.
Sometimes, I like eating Chinese food.