I've heard of "che buttà?", which I understand is quite slangy.

Che si dice zio? = what's up dude? (zio means uncle, and is an equivalent to dude,bro, mate....) Hey bello com'è? = litteraly means "hey "handsome" what's up? ( we say it naturally, even if it could sounds "odd" to english native speaker; we doesn't mean litteraly as an adjective; we just say "bello" like you say "bro" etc... ) We also say "man" like an italian word: Hey man com'è? An other good one: Wee zio tutto a posto? An other "dude" word it's used in certain parts of Italy is "Biondo". It means "blonde hair" and we use like your "bro, dude, mate,..." (even if you aren't blonde haired xD xD xD ) Heyy biondo! Com'è?

-- come va ? (How is life going on for you ?) You might also hear " tutto a posto ? ", which I would not suggest, as in my opinion has inside an implicit requirement to answer: "si!, tutto a posto", therefore is just 100 % formality, in a sentence that is not formal at all (lack of form and of substance).

Che si dice? = What's up? Allora...novità? = So...what's new? Come andiamo? = How's it going?

I can add : "come va la vita?"