Of course, while on vacation, you want to do some shopping. Depending on what you're after, there are several ways to go about doing this and having a good time doing it. You can practice a Mexican hobby of the haggle, or go someplace that just has prices of things and that's how much they cost.
You'll find that most places near the Malecon are all fixed price places. There are a whole slew of jewelry stores (opal and silver are the most common), trinket shops, and a lot of art galleries in this area. Most of the trinket shops all have very similar stuff...painted glassware, pottery, crappy tourist junk, shot glasses, etc. Jewelery stores tend to specialize in silver goods. As you've probably read somewhere or another, make sure it's stamped .925 to indicate the purity. If it's not, don't buy it. The art galleries are pretty fantastic. They tend to showcase Mexican artists of every genre. There is a lot of beautiful art available if that's what you're shopping for. Towards the far south end of the Malecon, across the street from the Palacio Principal and its plaza, there are usually local artists that set up their works and sell them right there. The prices are quite reasonable and they're usually willing to work with you on price. They also have some very beautiful work that to my untrained eye had a good price/quality ratio. Along the Malecon you'll encounter a lot of people walking up to you with trinkets and cheap jewelery in hand. You can do some haggling with them, although since we didn't buy anything from any of them, I don't know how far you'll get.
I was most impressed with the art at the south end of the Malecon but that aside there are but a few good deals to be found if you look for them and I wasn't overly impressed with the items their prices.