My son was a little behind in his speech as well when he was younger. Spend alot of time talking to them and make them ask for things rather than pointing...I find though they will eventually grow out of it and pick it up themselves. I found when my son was attending nursery and interacting with other kids his own age his speech came on leaps and bounds.
read lots of stories and speakto him properly no baby talk! also make eye contact and come down to his level when speaking to him! dont worry though he will speak when he is ready all children develop at their own pace!
also if u enrol him in a day care centre for a few hrs a day/week he willl come on great as listening to other children speak wil be great help and he will have to ask carer for what he wants etc! try reading repetative books like someone bigger, we're going on a bear hunt etc kids lovethose sort of books and after few times reading it he should start repeating lines in book
read to them and no baby talk. I talked to my daughter like regular person for the most part and she started talking.. well really really talking when she was about one. All kids go at their own pace though. Lots of verbal communication
Two yrs old is ok, although many speaks earlier. But my child started to speak at his three years, now he's very talkative!
Asides from all that has already been suggested, you really have to work on yourself. It does take time to get them to talk and alot of patience, no more accepting nods and pointing to items as an answer.
Try little fun games when out, eg, everytime you see a red door, he has to say red door. Then blue, yellow etc. Make up little songs that he can join in with, bathtime song, laying the table song, just loads of silly things that are fun, but make use of his words.
Also don't stress about it, as long as he is happy and healthy that is the main thing.
Shut computer off and spend time talking to child . . . .
Phonetics I believe is the best system to teach a child how to speak carefully. Lots of good advice here so you should take some of each of the answerers.