One of my go-to books for inspiration and practice ideas is Chris Orwig's People Pictures. In it, you'll find a plethora of fantastic imagery, as well as some very insightful advice for taking photos of....you guessed it! People.
I think one of the things that I really like about his works is that they are all very real. There's substance. The photos are engaging, despite the fact that I don't actually know the person in the image. There's something else too: Chris has style. His photos look very well balanced, immaculately lit, and have a slightly subdued color palate.
He gives me something to aspire to.
I'm also impressed by the variety of mediums that Chris implements in his portraiture. Looking through his website you'll find photos made with everything from a Canon 5D Mark II to a 4X5 film camera.
So check out Chris' book for some engaging reading, tips and practice exercises to take your portrait photos to the next level. In addition, take a look over his work at http://chrisorwig.com/. You'll find several galleries of photos, some links to Lynda.com courses and even a TedX Talk.
Have a super fantastic weekend!