I've posted the Santa info several times, and at least a couple of those times have been in the Christmas Superthread (when in doubt, please always go to the Superthread). But I'll give it again.
Santa has an actual PhotoPass person at the GCH - he will usually appear there in the evenings, after 5 p.m. - roughly between 6 p.m. - 8 p.m. (that's when I have seen him in the lobby - maybe he is now there at 4:45 but I haven't seen him there that early). You can find out from the CM's at the front desk exactly when he will be there that day/night. He sits for intervals and then takes breaks. When he is on breaks, sometimes the carolers come and perform on the other side of the giant tree.
Santa appears without a photographer in the Paradise Pier lobby, usually in the morning hours.
Santa appears at the
Disneyland Hotel by a rather elaborate display/backdrop, but the last time I checked there was not a PhotoPass person with him (not sure if that has changed). He is usually there in the mid-late afternoon.
Santa is at the Reindeer Round-Up in Disneyland, on and off through the day, and in Paradise Pier in California Adventure - both of those set-ups usually have PhotoPass people, I think.
As for the Winter Sweater/holiday characters, I have mentioned before that I've seen them in Toontown and at the start of Main Street, in the Town Square area. I think there may also be a winter sweater or two at the Minnie & Friends breakfast. Pluto in his reindeer ears is usually at the Round-Up.
