I would consider Amazon a major influence in my purchasing. I rarely leave that site without adding a book or toy for the kids to the wishlist.
Also, the grocery store coupons can influence what I buy. I buy cold medicine and Tylenol and they give me a coupon for Kleenex. I run back and get some Kleenex.
We consult Consumer Reports before we make any major purchases.
I hadn't thought of it before, but the maps that rate trails at the parks by the degree of difficulty will influence which trail I hike.
I also choose field trips for the kids based on my own algorithm where I rate the tone of the literature - family vs. adult oriented, the distance from home, and the cost.
I'm sure there are quite a few more. I'll be thinking about this for awhile.