My 3yo was just evaluated today for her speech. She was in speech therapy through Early Intervention for about a year, but we took this summer off because we couldn't afford the gas to drive 30 minutes to therapy.
She apparently made quite a bit of progress on her own over the summer, as she tested 'normal' for her actual speech. I'm still waiting for the results of her articulation, to see if she will receive therapy through the school district now that she has aged out of EI.
I will say, that I think the BIGGEST help with developing her speech was reading to her, and having her 'read' with me. I will read a sentence, then have her repeat it. I go for two goals.... One is to get her to say as many words straight as she can, the other is to get her to say them clearly. I never do both at the same time though. So one page we will go word-by-word, and I will focus on correcting her articulation in the way her speech therapist showed me. The next page I will let the sound errors slide, but try to stop her from dropping words in the middle of a sentence, or to get her to say as many words straight as she can. When we started doing this in May, she barely had 2 word sentences and even I could barely understand her, and strangers couldn't at all. Now, she is using 5-7 word sentences, and is able to string sentences together when speaking on her own... I can understand her about 75% of the time, and strangers about 1/2 the time. A HUGE leap for her!
I would suggest asking her pediatrician for a referral for a speech evaluation through your school district. (She is too old now for Early Intervention, so you will need to do it through the school or a private therapist.) get her evaluated by a professional, and go from there. :)
Good luck!