Another great colloquial expression, other than to have a thing for is to be into or to be really into. It more or less captures the generality of range.
I am really into Swedish girls.
I am really into comic books.
I am really into sailing.
Cautionary note about both to have a thing for and to be into - because they have a certain possessive or aggressive connotation, I would think it odd if somebody used them with respect to, say, his sister, babies, etc. "I am really into my sister," just sounds bizarre at best. Especially if a man used it that way. Maybe less so coming from a woman. It is better for a man to say he has "a soft spot for" such things.
Also, just a point on usage, "I am really into comic books," is fine for talking with mom or grandma, but "I am really into Swedish girls," would probably sound coarse in such company. It's mostly a matter of subject, but the language, while not exactly foul, isn't exactly delicate either.