Please help me find a language to learn x)

Okay, I have made a pact that I would take up another language beginning in the new year and I am having great difficulty deciding which one to commit to!

Currently I live in Australia, speak English at home and have 8 periods of Japanese a week at school. 

Some idea's for languages I have tossed around include:

French:  I could take it up as an ab-initio IB unit beginning in 2010

Spanish: It's one of the most spoken languages in the world "seems" relatively simple compared to other considered languages.

Chinese: It's super useful with China's economic rise and could lead to future career opportunities


However I am open to any suggestions :) I'd prefer it to be a relatively main language with as many speakers as possible. I'm just interesting in hearing feedback and opinions on learning specific languages.

Any input will be appreciated! :)