Transition metal chalcogenides (compounds based on sulfur, selenium or tellurium) have long been known and explored.  Due to their reduced dimensionality, such compounds sometimes display charge density wave (CDW) transitions or, upon doping with magnetic ions, often reveal dramatic changes of their physical properties.  I will discuss two different effects due to transition metal intercalation on the properties of layered chalcogenide materials, TiSe₂ and TaS₂.  Although TiSe₂ is one of the first known CDW-bearing materials, the nature of its CDW transition remains controversial.  Recently the interest in TiSe₂ has been renewed by our discovery of the new superconducting state (SC) that emerges upon Cu doping.  Thus Cu_xTiSe₂ provides the first example of a system in which controlled chemical doping can be used to study the competition between the CDW and SC.  When Cu is intercalated between the layers of TaS₂, a CDW-to-SC transition is also observed, although the origin of this transition is apparently different in the two compounds, and I will point out the similarities and differences between Cu_xTiSe₂ and Cu_xTaS₂.  I will also discuss experiments on Fe-doped TaS₂ aimed at studying the sharp switching of the magnetization that we observed in Fe_xTaS₂ for x = 1/4.  For this particular Fe content, Fe_xTaS₂ orders ferromagnetically below 160 K and displays very sharp hysteresis loops in the ordered state when the applied field is perpendicular to the TaS₂ layers. The corresponding magnetoresistance is negative, and qualitatively reproduces the features observed in the M(H) data, by showing a sharp drop around the critical field for moment reversal.