Great thread. I'd just like to point out that sumimasen doesn't necessarily mean excuse me, however. A lot of Japanese words mean different things in different context, and sumimasen is one of those words. It's basically a word you use when you believe you have bothered someone. When you say 'excuse me' to someone, you're interrupting what they are currently doing, so that is why sumimasen is used. Sumimasen can also be used to apologise when you have inconvenienced someone or have asked them to go out of their way for something. Unlike gommen or gomennsai, sumimasen also expresses a feeling of gratitude. If you ask someone for a favour and they do it for you, you can reply with sumimasen and it would mean both sorry for bothering you and thank you. Sumimasen is also a more mature word than gomennasai, which you would use to your superiors or perhaps people you don't know when apologising. In short, it can mean excuse me, thank you or sorry depending on the context.
Here are a few other words and phrases I have picked up that might help
I don't know - Shirimasen
What - Nani
Where - Doko
Who - Dare (prenounced da-reh)
Which - Dore (prenounced do-reh)
When - Itsu
Everyone - Minna
Please - Onegai
Welcome back - Okaeri
Dad - Tou-san
Mum - Ka-san
Wait - Matte
Help - Tasukete
What are you doing? - Nani o ****e imasuka?
Nothing - Betsuni
Really - Hontou
One - Ichi
Two - Ni
Three - San
Four - Yon
Five - Go
Six - Roku
Seven - Nana
Eight - Hachi
Nine - Kyuu
Ten - Juu
Eleven - Juu ichi
Twelve - Juu ni
Thirteen - Juu san
Fourteen - Juu yon
Fifteen - Juu go
Sixteen - Juu roku
Seventeen - Juu nana
Eighteen - juu hachi
Nineteen - juu kyuu
Twenty - Ni juu