I've had fillers injected into those lines at the side of the mouth (Naso Labial lines) and was very pleased with the results.
There are many types of filler, Restylane, Perlane, Radiesse, Juvederm etc. Most are based on Hyaluronic Acid and last anything from 3 months to a year. I had Juevderm and it cost about �360.
There are many beauty salons who administer fillers and Botox, but I would suggest you only allow a doctor to do it. It's probably best to go with recommendations from those who've had it done.
Botox has been used as a wrinkle treatment for many years and as far as I know, there are no serious side effects. However, you should discuss any side effects with the cosmetic surgeon who treats you.