Helpful tool for dealing with your PDFs. With Mendeley you can:
Good for handling PDFs and other items like saved images or web pages. Doesn't have robust annotation tools (no native highlighting or sticky note capability for instance). With Zotero you can:
Read more about Zotero.
Dropbox is very useful for saving documents so you can access them from multiple computers and mobile devices. Create folders to share documents with a group. It doesn't have the same annotation and note-taking features as the above tools.
Add PDFs, take notes, and cite documents as you write. (Citation feature is fairly clunky.) Search databases and pull out PDFs. Note: This feature doesn't work well with certain MIT Libraries' licensed databases.
iPad/iPhone app for organizing files and annotating and highlighting PDFs. Syncs with Google Drive, MobileMe, Dropbox, and more. Create your own hierarchy of folders to save your documents into. Highly recommended for reading and annotating scholarly articles.
Fast PDF reader for making and saving annotations and highlights.
To manage photos, try these tools: