I was just offered the role of Caliban in The Tempest for a production that's going up in March, and, instead of making a firm decision, I decided to spend time researching the role. I thought I knew most of the major Shakespeare sites on the web, but there are so many that it's inevitable some get missed, and I had never seen Open Source Shakespeare, which is a great site providing statistics, a concordance, an advanced search, and all the plays, poems, and sonnets.
Of course, plenty of sites offer these things, but I like how easy it is to filter and manipulate information here. For instance, if I did accept the role, it might be useful when learning them to view all of Caliban's lines, and this site offers a range of ways they can be displayed: truncated, complete, or with cue lines. The last is actually really handy for memorization.
Wonderful the stuff you can find out there on the internets!