I agree with Jen.
I read to my ds a lot, talked to him about everything that was going on around him, sang to him, etc. It seemed that my mouth was talking all the time! I was thinking about flash cards, too, but since I took care of my baby myself, after doing all of the above, I didn't have the energy to use flash cards. And he still learned a lot without them. At 6 months he could say 4 words: mama, papa, yumyum (yummy), mam (eat). At 12 months he started talking. By 14 months he started to talk in short sentences, already knew more than 300 words and in two languages! Now at 17 months he talks in sentences, all day! Also he picks up a lot of new words from us, his books and children CDs.
If you have the time and the energy to use flash cards, I think it's ok, too. Because not every children are the same. Of course there some pros&cons about them. But the important thing is to talk & communicate with your baby.