Medical Doctors:
Dr. Sato (canon), Turncoat, and mentioned in "The Longest Day" part 1 -- Thicker than Blood.
Dr. Daniel Goldblum (and Family) - Goldblum is introduced in "Sacrifices" Part 1. "Sacrifices" Part 2 he mentions his family. -- "Reunions", referenced in "Lethe", The Battle Below, The Longest Day part 1, The Waiting Game, Odd Couples. -- "Waystation".
Dr. Alan Bremer - "Sacrifices" Part 1 - colleague of Dr. Goldblum.
Clancy - a paramedic on site during the hotel fire in "Turncoat"
Dr. Milionis - "When the Bough Breaks" part 2 - Hope Ramsey's doctor.
Dr. Howard - "The Darkest Hour" part 2, "Aftermath" part 1. Employed by Xanatos.
Dr. Emily Gray - "Waystation", "Of things to come", "Through the Storm", "Unions".
*
Scientists:
Dr. Anton Sevarius (canon), Consequences -- mentioned in "The Rising" part 1, Beginning Again, "When the Bough Breaks" parts 1 and 2, Odd Couples -- "Unions".
Dr. Josephine Addams (in San Francisco)- noted psychiatrist and expert in mass-hypnosis. "Blood Moon"
Dr. Yvette LeBlanc (in Washington) - a government expert in biochemical toxicology. "Blood Moon"
Dr. Rupert Fenton and Dr. Arthur Kendall, "A Study of Phase-Inverted Sonic Interference". Dr. Fenton's lab was the one broken into by Unseelie the night before "The Darkest Hour" part 1.
Marian Reynolds (the Egyptologist) - mentioned in "Disobedience" - lives next door to Jeffrey Robbins. They're friends. She's in Boston at the time that Sekhmet raids her house. Also in Season three, "History's Forgotten".
Professor Arminius Fenn- the man in charge of the Dinas Emrys archeological dig. "Professor, you claim to have discovered that this hill is, in fact, hollow. Could you explain?" - Pendragon, "The Watching Eye"
Dr. Lydia Duane - (canon), "The Watching Eye"
Dr. Arthur Morwood-Smyth - (canon), "The Watching Eye"
Professor Jeremiah Bowen - "History's Forgotton" - colleague of Marian Reynolds.