As a scalpel is to a surgeon, a media list is to a publicist. Often the strength of a list can supersede a publicist's overburdened schedule or lack of creativity. Many publicists who move on from stints with a publisher have a distinct advantage because they take with them lists of journalists carefully cultivated by many within a publishing house.
There are those lists, and authors are wise to consider this when interviewing publicists. But. You might want to consider those publicists who customize a media list for your project. For a parenting book centered on the younger mother, Mr. Obie Joe compiled a media list that started with parenting magazines, and then delved into regional parenting magazines, and then went to online communities/magazines.
Another tip: when negotiating the contract, ask for a copy of the media list used for your project. Not all publicists will share the list with you, but at the least, most will give those aspects of the list most relevant to your project. From there, take that list and make sure you keep in touch with those on the list, via e-mail regular mailings, or personalized pitches.