pngmart（免费有版权，素材资源还算丰富质量较高，访问速度快）
stickpng（免费有版权，图片精致适合找logo，访问速度慢）
StickPNG is a vibrant community of creative people sharing transparent PNG images which you can download for free and use in your personal non-commercial or educational projects.
觅元素（免费无版权，国外素材特别丰富，有每日下载数量限制）
觅元素专注于提供高质量版权素材图片免费下载的网站，提供优质png素材、高清背景素材、图片素材、设计素材，找高质量版权素材就来觅元素.
FreePNGImg（免费无版权，素材种类丰富需英文搜索，访问速度慢）
Download free PNG images, pictures and cliparts with transparent background in best resolution and high quality(HQ). Available for Mobile, Dual Monitors, HD, Fullscreen and Widescreen.