EndNote Web Mobile: Look up citations via your mobile device.
Mendeley: Free citation management program that works on your desktop & the web, with group collaboration features. Sign up for a free account here: https://www.mendeley.com/
Zotero: Free citation management program that works on your desktop & on the web, with group collaboration features. Sign up for a free account here: https://www.zotero.org/
Doximity: The physician's private network, accessible wherever you are.
Webicin@: A curated set of online medical resources in social media for patients & medical professionals.
Anki Flashcards: Content-agnostic flashcard creating program that supports images, audio, videos and scientific markup (via LaTeX). There is an UpToDate add-on available (see the Clinical Resources tab).
Want to know more about taking notes? This blog post describes 5 ways especially for medical students
BrowZine: Combines & arranges individual articles from databases in an intuitive newsstand, then delivers them to you in an easy-to-use format on iPad or Android tablets.
Docphin: Stay up to date on the latest medical research in your favorite journals for iOS & Android.
Evernote: Save your ideas, search by keyword, tag or even printed & handwritten text inside images.
PDF Annotation Apps: Includes links & summaries of free & paid apps. From iMedical Apps.