Digimap
Current and historical maps of the UK on a range of scales using Ordnance Survey data. You will need to register for an AUB account on first use.
RIBA pix
The Royal Institute of British Architects' image collection of over 100,000 photographs and drawings.
Artstor
Artstor contains over 2.5 million digital images relating to the arts, architecture, humanities, and sciences. These are all cleared for educational use and have the information needed for proper citation.
RHS Digital Collections
Digitised collections belonging to the Royal Horticultural Society, spanning over 500 years of gardening history and science.