Kerm, Latin names, of course. Then there's memorandum and agenda are two I know of.

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Now that I think of it, I'd rather say memoranda, but I would use agendas over agendae.

I would definitely say memoranda, but not agendae or vetum (vetum? I'm having trouble remembering how to decline that)

"veto" was actually a verb, so no wonder. :p

Here's a few -us nouns that come from Latin, where the Latin declension doesn't sound right in English:
genius (genii?)
campus (campi?)
onus (onera?)

My personal opinion is that, if a loanword becomes a part of common, daily English language to the point that it's no longer considered “foreign” and italicized, then it should not be exempt from normal English rules. There's no reason to complicate and bend English grammar to match every language under the sun; it's already complicated enough that people hardly get it right as it is. Though, sadly, English is probably too far gone by now for this to be anything more than a moot point.

"agenda" is actually plural (neuter nominative plural of the future passive participle of ago, lit. "things to be done")
So to repluralize it "agendas" would seem correct here.

Calcdude, dammit, I knew that too, and I had totally forgotten. Thanks for that, you're absolutely right. Travis, I agree that English rules would ideally apply universally to English (not that they do anyway, with all our crazy, wacky irregularities), but I personally like treating direct loanwords specially; maybe it's me specific brand of pedantry.

I never used Fora but I saw some people, especially dutch people, using it in the past. I personally always used Forums. There used to be a time where several people used "Fourms" too.

I usually call it "fora" when writing, but I almost always say "forums".

"Data" is another interesting one. Cambridge assures me it is singular and plural (rather than "datum" being the singular). Do you favour "the data are analysed" or "the data is analysed"?

I usually say "the data is analyzed".

I say "the data is analyzed".

Fair enough. Back to the topic of forumz...

I side with the people who say that, once a word has been integrated into a new language, it's no longer subject to the grammar of the language is was borrowed from. Unfortunately, I'm afraid English lacks the kind of consistency necessary to support that kind of action. English is too much of a "YMMV" language that tries to preserve needless dialectal differences just so everyone can have an excuse to speak however they were raised to speak. These dialectal differences, of course, include blatantly wrong syntax and spellings, and slaughtered pronunciations.

I say use "fora" just to be overly-pedantic and annoying to everybody else. Why not? Other people speak their own personal dialect of English, anyway. They don't care how stupid they sound, how their bad habits are discouraging literacy, or how much they're damaging the already inconsistent orthography of our poor language. It's total Anarchy.

Maybe "fora" would at least make them think about the etymology of the word, and encourage them to think a little more before they speak. On the other hand, you'll probably just get a few weird stares.

Yay, I love being overly-pedantic and annoying! I'm glad we're in agreement on that.

We are so in agreement.

You know, I often get accused of being archaic or even Shakespearean for saying, "It was I" as opposed to, "It was me." I have to take the time to explain how you aren't supposed to make yourself the oblique case of indicatives of "to be."

I don't see any reason for people to think that that's archaic; being grammatically correct and being archaic are two very, very different things.

http://grammar.quickanddirtytips.com/grammar-linking-verbs.aspx

Kerm's right, the "It is I" form is correct even if it is not in popular use. Doesn't it suck how pedantic you can sound just by speaking proper English?