This seems like a reasonable survey article: http://projecteuclid.org/DPubS/Repository/1.0/Disseminate?view=body&id=pdf_1&handle=euclid.bams/1183547543
Also there is a book by Deitmar and Echterhoff - "Principles of Harmonic Analysis", which I found quite readable, but that treats coefficients in $\mathbb{R}$ only. But this book is probably more likely to be useful for graduate students.
