I got Tom Baker's autograph (Doctor number 4) on 16th October 1997 when he was doing a book signing in Bookends, Christchurch for his autobiography Who on Earth is Tom Baker.
I got Elizabeth Sladen's (Sarah-Jane Smith) autograph at the "Space Weekend" do at Castle Bromwich Hall Gardens, Birmingham on 27th June 1998.
Nicola Bryant's (Peri) autograph was from the same event, but the following day.

I'll put up some photos, from the event, of Nicola and Elizabeth as soon as I get them developed.

Hopefully I'll be able to get one or two more signatures in the future.