As you know if the believers want to follow the right way, he should be close to an Islamic group so as to urge him to Islam. What books and tapes would you advice me to buy?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Indeed, good company provides tremendous support to be steadfast on the right path. Such company helps one to be firm in goodness at the time of disaster and reminds him when he suffers from carelessness. Therefore, the Prophet (Sallallahu Alaihi wa Sallam) made a good companion like the musk seller; everyone who accompanies him will get benefit of his good smell. Likewise, one benefits from his good friend at least by his greetings, shaking hands with him, having good words from him etc. Know that a person is naturally inclined to follow and to imitate his friends. The Prophet (Sallallahu Alaihi wa Sallam) said: "A man follows the religion of his friend; so each one should consider whom he makes his friend" . [Reported by Imams Ahmad , Abu Dawood , al-Tirmizi with a good chain].
As for good books and cassettes, they are many; the most useful of all books is the Book of Allah and the sound Hadith of the Prophet Muhammad (Sallallahu Alaihi wa Sallam). So, recite the Qur'an as much as possible and comprehend the meanings of the verses. Also you should keep reading the Sahih al-Bukhari, Sahih Muslim, Riyadh al-Saliheen, the books concerning the biography of the Prophet (Sallallahu Alaihi wa Sallam), the biographies of the companions of the Prophet (Sallallahu Alaihi wa Sallam) and their successors.
Allah knows best.