Here is a small sample of what Yoshi can say. Since I get a lot of people asking how to teach their quakers to talk, I thought I could answer that as best as I can here.
To be honest, it really depends on your bird and the amount of time you spend with him/her. Yoshi loves attention and he quickly figured out when he started talking that he got lots of positive attention. I also play a lot of games with him and sing to him everyday. I don't know if this has anything to do with it, but I keep a radio on for him all day as well. He loves Bob FM mainly because they always play Blondie and Madonna! You can tell the songs he likes because he will sing along to them...not the actual lyrics but parts of "Twinkle twinkle little star".
To get him comfortable with the whole foot-shaking thing, I started by playing games with his feet. When he was on my shoulder, I'd touch his toes and say "What's this?" and tell him "Toes!" or "Toe Toes!" Then I started switching it up and I'd grab his foot and say "Nice to meet you!" and eventually he just started offering it to me. He also likes the "Gimme those toes" game where I say that, grab his foot and pretend to eat it (complete with nom nom nom sounds).
So really, the secret to Yoshi is just spending a lot of time playing and keeping him entertained. At first I think he started with regular sounds I make...it's been a long time but I think he was copying my sneezes and hiccups before the actual words came out. He was mainly saying things I was trying to teach him and then he was picking up on things I didn't realize I said as often as I do! Eventually he got to a point where he would make up his own combos of words that I KNOW I've never said before! One example is that he says "Sweet baby" which probably came from "Hi sweetie" and "Hey baby" or "Ooooh baby!" My favourite is his supposed insult. He knows all sorts of phrases like "You're cute", "You're a good boy" etc. He also knows "poopy" and "wanna peanut?" and at some point he decided to mix and match these things to say "You're a poopy nut!"
If there is interest, I might be convinced to start a Facebook page for Yoshi...he seems to have acquired a nice fan-base for it!