A very comprehensive website about birds by the Cornell Lab of Ornithology. High quality photos and information and good side-by-side comparison of similar species.
Good comprehensive source of butterfly photos, specialising in Ontario but extending to Quebec and the Maritimes. Including links to the Ontario Butterfly Atlas. By Rick Cavasin.
Many Google wild flower searches have led me to this website by Walter Muma. One of my main identification sources. Fairly comprehensive and seems quite accurate. Photos are 'old school' (meaning small).
Barry Robertson, a neighbour on Otter Lake, gave me this list when we first moved there and I refer to it frequently. I use it mainly as a cross reference to check if others have observed a certain plant in the area, and by what common name they refer to it.
A map-referenced listing of trees with good photos of their leaves. Produced by the Ontario government to encourage the planting of trees native to each region.
Try uploading a photo here and letting Google search for similar images. This is worth a try for species you haven't a clue about! Sometimes some of the selected images give you a starting point for searching in the more specialised web pages.