I am an Android guy, so the one app I invested in was Moon+ Reader Pro, https://play.google.com/store/apps/details?id=com.flyersoft.moonreaderp&hl=en
It works perfectly for my needs, plenty of options for those who want their ebooks to look a certain way. Although the main option I use is the Text to Speech(tts) feature. It will read the ebook to you, I use it when I walk to work and while at work using my Bluetooth ear piece. Now the default TTS voice isn't the greatest sounding, but there are plenty of them out there for you to try. Recognition of words is pretty good, while it does have problems with abbreviations or acronyms, and names, it gets probably 95 percent of the words correct. So with the TTS option, I can buy an ebook and get an audio book for when reading is unsafe or not feasible.
The next thing I use is a website called FictFact.com. I enjoy reading books where the main characters are continued throughout a series. Probably the most famous or popular of these are the Jack Ryan character from Tom Clancy or the Dirk Pitt character from Clive Cussler. Well that's where FictFact comes in, it allows you to keep track of your favorite series by character, or author. Here is my list of series, http://www.fictfact.com/list/jtintle/9306/ALL
Finally I needed something to keep track of all those ebooks, that's where Calibre (http://calibre-ebook.com/) comes in. It's a library management program. It keeps track of your ebooks and allows you to sort, search and sync all your books. It does alot of things anyone who owns tons of ebooks can use. Check them out for more information, its also an open source program.
I hope this little post sheds some light on a few things that help you with your reading needs.