Today's app is really easy to write about, as it's one I already know and love. RefME is simply fantastic for collecting references. It's so very easy - you can use a web clipper in your browser, you can search by title, author, or ISBN from within the service quickly and easily, or you can scan the barcode on the book! For undergraduates, this is so much easier than exporting references in RIS format from whichever database they are in (and they're not usually in a database, they're usually on Amazon...or Wikipedia...) It's even easier than having to change your settings in Google Scholar to the correct reference management software.
In short, I love it, and I use it myself.
The only issue with RefME is that is doesn't currently have a cite-while-you-write component, although you can generate a perfect reference list and the layout of your citations is shown for you as well. To my mind this makes this more of an undergraduate resource, where you might not be handling too many references per assignment. On the other hand, you can export out to Mendeley, Endnote etc. so you could then use these services for cite-while-you-write if you so wished.
One final really cool thing about RefME is that they accept individual institution referencing styles and include them in their service. So if your institution has an agreement with RefME, you may very well find the correct style is already pre-loaded and ready for you to use.