Imgur.com is one of the best, if not the best, sites to upload that image you're about to share with a gazillion people. The site is very simple and robust, yet incredibly functional, and, most importantly, allows all uploaded images to be embedded on other sites without complaining about hotlinking. It is the service used almost exclusively for sharing pictures on reddit.com (hi all redditors!). Imgur started as an anonymous one-time upload service but later introduced account support, which was probably the most frequently requested feature.
Today marks the arrival of an Imgur Android client with account support baked. I'd like to point out that there are actually 2 other imgur apps on the Market already, but neither of them offers the ability to log in.