In this case you have two backdoor draws. If the turn and river both come spades, you'll have the nut flush. If the turn and river come a king and queen (in either order, of course) then you will have a straight.
Backdoor draws' value is typically estimated at 1-1.5 outs, so they're generally not worth pursuing alone unless the pot is extremely large. When combined with other draws, such as overcards, or a gutshot, their value can often tip a fold into a call or a raise.