If its a concern people will bring gifts you already have or don't fit your taste you can always send out the invitation with a gift regisry for a specific store or keep in mind you can return any items you recieve or exchange for items you needed instead. I really don't know if there is a way to request a money tree instead of gifts without sounding (sorry to say) tasteless. Personally I always go into those situations with no expectations and appreciation for what ever is done for me. I hope you have a great housewarming party and enjoy your new home. Fro's suggestion could be good if you have a close family member who knows all the attendees well enough to approach them about it.