One of the most usefull little few-cent devices I keep on hand is the 2N7000. This is a FETlington, a small fet that replaces small bipolar Darlington transistors, The advantage is that the input is 5v logic compatible (max40v) and of course, high impedance of a FET and will handle 200ma max. drain current and operate devices (relays etc) up to 60v rating. I know there are chips that will do a similar job, but if you only need that one or two relays etc. it is quick and cheap.
Al