Kumpel, Kerl, Freund, Kamerad.

I bet you want to know how you'd say things like "What's up dude?" or "How's it going buddy?". All the words Munkelman wrote down are correct translations of buddy/dude, yet honestly in german we hardly use them when directly talking to friends. The only term that is really used in direct speech is, as Jenny already said, "Alter", but only among young guys. You might hear something like "Was geht Alter?" (What's up dude?) or "Alter!" (pronounced as Alder; translates directly to "Dude!". But careful, "Alter" is ONLY used when your calling that someone directly. You can't say "Er ist mein Alter" for "He's my buddy." because "Er ist mein Alter" is a impolite way to say "He's my dad." If you want to talk ABOUT your buddy you'd use "Freund" or "Kumpel". It's also possible to use "Kumpel" sometimes when directly talking to someone, but it's not the same with "Freund". If you directly address someone with "Freund" or "mein Freund" it sounds in a strange way formally intimate except for some rare situations. Don't ever use "Kamerad"! It's only either used for your fellow soldiers in military service or in some situations in an ironic way. There are two more ways to translate "dude" which are "Kerl" and "Typ". You should be rather careful with those. "Dude" is a rather neutral way to talk about some male person. "Kerl" on the other hand means "a very masculine guy" but often with a negative meaning to it. You might hear "Dieser Mistkerl!". "Typ" is a little bit more neutral but not much. If you talking about someone as "Typ" it depends really on your tone and on what you are saying about him as to what connotation the term gets. A girl might say "Der Typ ist so süß." while someone else might say "Der Typ hat sie doch nicht alle!". With "Typ" you have to be especially careful to be out of hearing range of the person you call "der Typ". It's not actually an insult, but it's very impolite to talk about someone as "Typ" while the person can hear you.

Or even "Alter" (that corresponds well to dude...), but it's just used when you speak directly to another person (a person you should be familiar with)...like: "Hey Alter...." But I would say that you can't do (or say ;-) anything wrong with "Kumpel".

I don't know