well rc i find interesting, especially once the blood runes and soul runes come out.. aren't bloods around 500ea, u could just sit there and pay people half the bloods for a run, they would still make more cash than nats
But in terms of useful and cash i would say smithing, the rune/addy armor will be useful for pking, so that works for clan members/friends, and rune is a somewhat easy item to sell
but blade u should do the new achievement diary at least easy, the new armor gives a chance to double ore mined (up to coal) or bars smithed (up to steel)