It's my suggestions:

Hello/Hi - Cześć
How are you - Jak się masz
Bye - Pa, cześć
Maybe - Może
Excuse me, I am sory - Przepraszam
Thank you very much - Dziękuję bardzo
Happy birthday - Wszystkiego najlepszego z okazji urodzin
Sweet dreams - Słodkich snów
Have fun - Baw się dobrze
I love you - Kocham Ciebie
I miss you - Brakuje mi Ciebie

If you have any questions mail me: mirpoland@interia.pl

We usually say "Kocham Cię", not "Kocham Ciebie", but in my opinion two are correct.

What's the Polish for 'get lost' (go away)?

For example when someone is hassling you for money on the street.

Odejdź ode mnie.

How would that be spelt if an English speaker wanted to say it? This is the problem with Polish. I see a word or phrase and have no idea how to say it. Too many consonants together!

Odejdź ode mnie /odeydzh ode mneh/
You can also say: spadaj /spaday/ when someone will be very insistent.

Hello. I'm new on here, and new to the Polish language. Just a minor point, Simon. Your translation for 'Good evening' should be 'dobry wieczór, I think (accent over the 'O'). Still, a very useful list.
I have to learn Polish, now, as my work involves conversing with Polish people on a daily basis. This looks like a great site.  I will probably be asking a lot of questions in the future.

Visitors might like to see a list of useful Polish Phrases alongwith MP3 / WAV files to listen to:

http://onestoppolish.com/useful_polish_phrases.htm

@ Kasia I agree, "Kocham Cię" better

Ciebie is used for emphasis. "Kocham Cię" is normally used to say "I love you", but if you want to say you love the person you are speaking to and not somebody else you would say "Kocham Ciebie". Ciebie is also used after prepositions as in "Czekam na Ciebie" (I'm waiting for you) and "To jest dla Ciebie" (This is for you).

If you want to tell someone who is harassing you to go away and add "or I'll call the police", would you say "Odejdź ode mnie ale wzywam policję", "Odejdź ode mnie ale będę wzywać policję" or "Odejdź ode mnie ale wezwę policję"?

What are the Polish names of the letters q, v and x?

"Odejdź ode mnie albo wezwę policję"
or - albo

"but" here does not fit

the difference between those two above, is in grammatical case.
In this example, makes no diferent at all.
Just pick form is easier for you to say
~koham che~ vs ~koham chebye~

Actually, I would say that "Kocham cię" is more correct. I was taught that we should use longer pronouns at the beginning or in the middle (when it should be emphasised) of the sentence. Also, they are used when we reply with only one word, for example:
- Kogo kochasz?
- Ciebię. (NOT: cię)