This is not meant to be an exhaustive list of DX clubs. But these are a few of my favorites:
Hoosier DX and Contest Club (HDXCC) - my friends in Indianapolis
Lone Star DX Association - my new home
Spokane DX Association (SDXA) - my "home away from home"
Northern Illinois DX Association - very near to where I used to work
Northern California DX Foundation - these folks are very important sponsors of DXpeditions
International DX Convention - this annual event in Visalia, CA is one of the largest gatherings of DXers