Hi Herring,
It's a bit bleak in winter, but the Harthope and Ingram Valleys are good - there's a decent chance of Hen Harrier on the moors above the valleys, and Red Grouse are easy; look for redpolls in the alder woods (fair chance of Mealies among the Lessers). Dippers on the streams of course.
Hulne Park in Alnwick usually has a few Hawfinches, though they can be elusive.
The Milfield Plain around Doddington (3 miles N of Wooler on the B6525, and the minor road out NW from Doddington to Nesbit) is good for geese, usually a thousand or two Pinkfeet and a few hundred Greylags; scan carefully for others among them, last year there was a Snow Goose among them for a week or two.
Kyloe Wood inland from Holy Island can turn up surprises; limited parking at NU 062 392, walk in. Make sure you don't get lost in there though, the forest road layout is confusing!! Very nice place, huge conifers (50m+ tall), good chance of Crossbills and lots of Siskins, usually quite a lot of wintering Woodcock too, and the odd raptor or two.
The Long Nanny 1½ miles south of Beadnell / 1 mile north of Newton Links House (car park) currently has 5 Shore Lark and about 40 Twite on the saltmarsh just down from the footbridge (NU 228 272).
Have a nice trip and don't forget to report what you see!
Michael