First off, for some basic information about the test and its format visit the official TOPIK website.
(view the English version of the website by changing the language in the top right corner of the page)
The TOPIK exam is divided into four categories: Vocabulary/Grammar, Writing, Listening and Reading.
You might find the following resources useful in preparing for each section:
- Korean Grammar in Use - Intermediate - contains most, if not all, of the grammar you'll come across on the exam
- Seoul National University - Korean 4 - very useful for TOPIK intermediate level vocabulary
- The Yonsei textbook series is also helpful, levels 3-5 will be useful for this exam.
- Haru Korean - post unlimited sentences and have them checked by native Korean speakers
- Talk To Me in Korean - check out the "Iyagi" series, it's excellent for intermediate level listening practice
- For more advanced level listening check out Korean news websites such as MBC. Many feature news clips along with transcripts.