Here is a list of books that I've collected about learning Afrikaans which you might find helpful.

Teach Yourself Afrikaans – Lydia McDermott
This came out in 2005 and comes with two CDs. This and Colloquial Afrikaans (see below) are the best books avilable I think. Highly recommended.

Colloquial Afrikaans – Bruce Donaldson
This is an excellent book. Bruce Donaldson is a professor at the Department of Germanic Studies at the University of Melbourne and also wrote the Colloquial Dutch book in the series. Ignore the reviews on Amazon, they all seemed to have tried to learn the language just through the CDs. Highly recommended.

Teach Yourself Afrikaans – Helena van Schalkwyk
First book I used. It's pretty good, but a bit dated and doesn't come with CD or cassette.

A Grammar of Afrikaans – Bruce Donaldson
It costs £100 but it is excellent.

The Development of Afrikaans – Fritz Ponelis
An interesting and comprehensive study of the development of the language with selected texts illustrating the linguistic changes.

A Reference Grammar of Afrikaans – George Carcas
For £5 this is an absolute bargain. It’s only 48 pages long as well. Recommended.

Afrikaans: A Handbook and Study Aid– Beryl Lutrin
Not sure how I found it but it cost £5 including postage from South Africa. Excellent little book really, explains the grammar so well. Highly recommended.

Teach Yourself Afrikaans – MPO Burgers
This was first published in 1957 and it shows. Still, it is comprehensive and I bought it on Amazon Zshops for £5.

Learn to Speak Afrikaans – PWJ Groenewald
It’s an old one based on the 1,000 words methods. You can buy it cheaply online and in some bookshops.

Afrikaans Self-taught: By the Natural Method with Phonetic Pronunciation (Thimm's System) – Leonard van Os
First published in 1927, just been republished. Has phonetic pronunciation guide. It's cheap.

Painless Afrikaans – George Holloway
Another old book from the 1960s. Apart from the hilarious title it's pretty decent actually.

Afrikaans audiobook
Two cassettes and phrasebook. Not much use to be honest.

A Dictionary of South African English
Well I like it and find it helpful.

Form and Meaning in Word Formation: Study of Afrikaans Reduplication (Cambridge Studies in Linguistics) – Rudolf Botha
I got this cheap somewhere. I haven't read it in details because it's a doctoral piece but it is quite interesting.

Brush up you Afrikaans – Jan Nieuwoudt Tromp
I bought this on Amazon Zshops. It’s unintentionally hilarious and very dated as it was first published in 1941.

Afrikaans – Conversaphone
One cassette and phrasebook. Bought online from USA when Internet shopping was in its infancy. It’s limited in its range but at least you get to hear it spoken.

Talk Now! Learn Afrikaans
I never liked this one, frankly.

Kommunikeer in Afrikaans 6
Was given this by someone on the Internet. It's a school book but not bad

Leer Afrikaans: Standerd 1 – H Askes
Bought this in Foyle's in London. It's quite basic.

Leer Afrikaans Makliker – F Strydom, M Heyns, S Potggieter
My grandmother in Johannesburg sent me this. Lots of texts in Afrikaans.

Afrikaans-English/English-Afrikaans (Hippocrene Practical Dictionary) – Jan Kromhout
This is really good.

Juta’s Pocket – Afrikaans-English/English-Afrikaans Dictionary
It's quite basic, it doesn’t show different usage of words.

Bookshops

Grant and Cutler on Great Marlborough Street and Foyles on Charing Cross Road have a better than normal selection of Afrikaans books offering teach yourself books, dictionaries and some novels, usually André Brink and Harry Potter.