I would suggest French. I just gave my French term end exam today and it was awesome! :D
On a more serious note, French is very easy to learn. Once you get the hang of some basics, it is simple sailing thereafter. However, the pronunciation is very difficult (in my opinion). That is because the spelling of the word and the way it is pronounced differ widely and it tends to confuse you. Also, different teachers pronounce the words in different ways (this is seen when one is learning from a non-French faculty). And, for me, French always seemed somewhat more well-known to the world in general than any other language (barring English).
I have friends who do German and they say it is easy too. You have to make more use of the throat, I think. The theory part is simple. Some say French is easier and others say German. If you are planning on taking science, I think German would be a good option. Because many research papers are written in that language and German universities are more famed for science than French.
Spanish grammar, my friend tells me, is quite similar to French. Once you know one language, the other is simple. So I don't think there would be all that much difference between the two.
I have read reports saying more and more people are taking Mandarin because of China's growing influence in the world and some say it may become the language of the future (I doubt it though). Like Pete says, the traditional script is difficult.
I know nothing else. :P
"If the bee disappears from the surface of the earth, man would have no more than four years to live. No more bees, no more pollination ... no more men!" - Einstein
"I like quoting Einstein. Know why? Because nobody dares contradict you." - Studs Terkel.
<@Ximenez> Sentynel: But i have a life? No. Qed.