Hi O.,
We did baby signing with both our kids, and my only regret is that I didn't do more!!! I started both kids around 7-8 months. My first child turned out to have unintelligible speech, requiring surgery at age 3 to help her talk, so I was so glad I'd done the signing. She also turned out to be a special needs child. My 2nd child turned out to have a very high IQ - he picked up his first signs a little bit quicker than his older sister had done BUT of course he had mummy and sister signing to him. As you can see, I have 2 very different children, and signing was great with both of them.
I used one package with my daughter, and then because I was bored by the time #2 came along 3 yrs later, I bought another package with more songs (my daughter ended up knowing 2 signs for some words, as one was based on ASL and the other on BSL).
One reason for choosing to sign, was that I was raising the kids bilingually, and I thought it would help them, because every item or concept would have 1 sign, even if the words were differend (eg sofa/couch/settee that's 3 words in just 1 language for the same item, then add the words in another language, that's 5 words for 1 item. Having 1 sign helped). Both my children were found to have excellent language skills (even the one with speech difficulties).
I used:
Sign-2-Me by Garcia. This comes from America and is based on ASL. I liked that it had a 'dictionary', a video (I'm sure they do DVD's now), and a wipeable chart you could use for the babysitter so that if the baby signs, they can look up what it means in seconds, or if they want to sign to your child, they can see which signs the baby knows.
Sing and Sign. This is from the UK and has LOTS of songs. It is based on BSL.
My kids watched both a lot on the telly, they loved it.
I know many people in the USA who use Signing Times, it seems to be popular.
I hope this helped.
A.
(we keep moving between the UK and Belgium)