Seth Johnson was lined up for a ~£4m move to boro in the transfer window, that might get rekindled. Dacourt may well be joining Roma for around £6m. Viduka has traditionally been linked with a move to Italy, they used to throw figures of £15m about but nowadays I'd say it would be more like £8-9m.
I guess Robinson, Kewell and Smith are the most valuable players, being young and with good talent. They would probably fetch the most money, but my advice to leeds would be to offload fringe players like dacourt, Johnson, Martyn (won't get much cash, but he's bound to have signed a fat contract when he was an england squad regular) etc, +viduka for the big cash (bridges can replace him). If they could get £20m for those 4 players that would be a step in the right direction I feel.
Mills would be a good buy for Arsenal but I can't see Leeds letting him go for under £5m.