Well, you’re from Oregon, so Spanish is a good choice.
Personally, I would learn Portuguese. This opens up, along with Spanish, almost all parts of Latin America. Not only that, it is very easy to make the jump from Spanish to Portuguese. IIRC, they were the same language until c. 1500, and are both in Iberia. But besides Brazil, Portuguese is spoken in Africa (Angola, Mozambique, Congo(?) and others) and I THINK, in parts of Southeast Asia (But that’s more Dutch, isn’t it?).
German, a language I attempt to speak, is also useful, for the scientists, and because of the emerging importance of the german speaking countries in the world stage. Ever since the reunification, Germany has been steadily increasing in importance.
Dutch and/or French - Because they got around!
Old English would be interesting. Just imagine your friends faces when you start speaking it and when they ask you what it is, you reply, English!
Generally, though, I would suggest looking back in your family tree, and maybe choosing a language from your past. That’s always interesting. Who knows, you could wind up speaking Irish, or Italian, or Polish.
Langauges I would recommend not studying (the following is STRICTLY IMHO):
Latin - they call it a dead language for a reason. While I’m sure you could find a reason to study it, it would be best to not select it out of hand.
Japanese - while you could have a •rare• affinity for it, the language is notoriously difficult, and it’s one of those things you need to start young on.
Languages with more than three predicates(I think that’s the word for “the”) - Zulu, Chechen, etc. If you study German, you’ll have trouble with their three, and I imagine you’ve had trouble with Spanish’s two. Native english speakers typically don’t handle predicates well. If you have problems with two or three, don’t even bother with insane ones like 9 or 12. Again, these languages you need to start young on. Although who knows, some people speak languages very well.
Languages that use a different alphabet/script/right to left rather than left to right form - Chinese, Arabic, Hebrew, etc. Nothing wrong with it, necessarily, but it is confusing (especially with ideographic scripts) and I would recommend ‘bulking up’ with more than two languages before tackling these.