Even though dropbox is probably simple enough to use without one, their "getting started" walkthrough is really the golden standard in my mind. Grooveshark is a

Even though dropbox is probably simple enough to use without one, their "getting started" walkthrough is really the golden standard in my mind. Grooveshark is a little different, but whenever you access the site from a new IP, their little tooltips are informative yet unobtrusive. They're constantly improving their product too so they help with that too. Just signed up for LeadNuke though, if anything comes to mind while I try it out I'll add it later.