If you were really trying to Anglify it you'd say "mediums"
But that's already taken.
"Medium" has several meanings in English. One is that of an underlying transport for information, in which case the plural is "media". That's the one we're talking about here.
"Medium" can also mean a person with psychic abilities who serves as an underlying transport between dead and living people. In that case, the plural is "mediums". The difference here presumably comes from the latin medium/media being a neuter-gender noun (i.e. dealing with inanimate objects), and this usage actually dealing with people. In the case of the last paragraph, the "medium" is an object. In the case of this paragraph, it's a person, and since the latin term didn't refer to a person, the later English rules for pluralization were used for the new usage.
And then again, it can be an adjective, as in "I'll have a medium (-sized) coffee".
Now, if some kind Northern Irish person would care to discourse on the pronunciation of "How now, brown cow", we can put this thread to bed...
