One of, if not the, best things about winter birding is a good raptor roost site. Given the time and choice I'd go to Stubb's Mill every time. Titchwell has provided a couple of good late afternoons in the past, but Royden Common has always been a little disappointing. However another site that can be good is Eldernell (cTL318991). Last time I was there with John Hague in February 2002 we picked up two Marsh Harriers, a ring-tail Hen Harrier (don't tell Prince Harry), a couple of Barn Owls, 6+ Short-eared Owls plus Merlin and Peregrine.
This site is accessed from the end of Eldernell Lane off of the A605 just east of Coates - see here for access details. As can be seen from this ariel view, the site is a mixture of rough pasture and fenland wash - sadly surrounded by mainly arable farming.
A Customer meeting in Wisbech today gave me the opportunity to drop in for an hour or so on the way home, though given the time (c13:45 - 03:15) and very dull, windy and damp conditions, I certainly wasn't expecting a big raptor and owl haul.
The large pool just south of the bank held Shoveler, Wigeon, Tufted Duck and Greylags, but the bulk of the wildfowl was on the washes with 1000s of Wigeon, 100s of Teal and good numbers of Pintail. Plenty of Lapwings and Golden Plovers also. Aside from the many Mute Swans, a small party of Whoopers flew over heading east.
Sadly the raptor count included only Kestrel (several) but a superb Short-eared Owl was quartering at sheep-head level for a good half hour apart from when being harassed by Crows. I strongly expect that a visit with more time (ie up to dusk) and in better conditions would produce more. A great site well worth a visit.