Death to Stock Photo
Death to stock photo is a newsletter focused service which send a list of staff picked high res images to your mailbox. You can subscribe to their newsletter from their homepage. APrt from that you can browse the library of images and download the one that you find suitable.
Free images is a website which includes premium images too but their repository of free images is quite decent with 350k+.
New Old Stock
New old stock is a tumblr blog which posts vintage stock photos for its users. They include a subscription option where they have mentioned clearly that most of thir images are optimized, cropped for easy usage.
Gratisography has a simple interface which makes images from various categories without page refresh and sports a magic search option where it displays relevant images to the text you write in the search box.
Magdeleine has a simple interface with photo of the day displayed in the full background of the homepage and also featured the photographer with instagram link as you can see in above screenshot. You can browse their library of images which looks very impressive.