The Kansai dialect of Japanese (関西弁, Kansai-ben) is spoken in -- surprise, surprise -- the Kansai area of western Japan, especially the big cities of Osaka, Kyoto, Nara and Kobe. The Kansai dialect is further broken down into a number of subdialects, the best known of which are the Osaka dialect (大阪弁, Ôsaka-ben) and so-called Kyoto language (京言葉, Kyô-kotoba). However, there are a large number of features common to (almost?) all area dialects, so that's what this node will concentrate on. Bear in mind that none of this means that Kansai people will only use the forms listed here: most are quite adept at speaking standard Japanese (標準語, hyôjungo), especially with big scary foreigners. But feed them enough sake and/or get them worked up over something, and they'll start to slip back soon enough...

Particles and conjugations

Standard     Kansai      Meaning
iru          oru         To be1 (kotchi kitoru, "Come here")
da, dewa2    ya          Copula (sugoi ya!, "Great!")
dewa nai2    yanen       Emphatic copula (ahoyanen!, "What an idiot!")
-su ka       -kka3       Polite question (môkarimakka?, "Making money?")
-su ne       -nna3       Polite answer (bochibochi denna, "I'm fine")
-nai         -hen        Negated form of verb (eg. wakarahen, "I don't understand")
1: In the rest of Japan, oru is a humble form used exclusively to refer to oneself, but in Kansai it can also be used (less politely) to refer to others.
2: In most other dialects, these become ja and jan(ai) in colloquial speech.
3: Used mostly in Osaka. Incidentally, these two example phrases are the canonical Osakan greeting and its reply, although I've never heard anybody use them unless teaching somebody Oosaka-ben...

Vocabulary

Standard     Kansai      Meaning
arigato      ookini      Thank you
chigau       chau        "It differs"; No; You're wrong
dame         akan        No way; Don't do it; Impossible
omoshiroi    omoroi      Interesting
hontô-ni     homma-ni    Really
baka         aho         Idiot
The above is of course not an exhaustive listing, there are large regional variations and slang phrases go in and out of fashion rapidly.

ObGTKY: I'm not a native speaker of Japanese, and the Japanese I speak I've learned in Tokyo. However, one of my best friends is from Kobe and I'm currently dating a girl from Wakayama with the cutest gangster accent, so I have been exposed to more than my fair share of Kansai-ben...