SINCE the collapse of communism and the parting of the Iron Curtain, Eastern Europe has become fertile ground for writers. Goodnight Mr Lenin (Picador $102), by journalist Tiziano Terzani, is a search for the ''corpse'' of communism. It takes Terzani through the vast continent, from Siberia and Central Asia to the republics of the Caucasus. On his way he meets Cossacks who hand him a letter to deliver to the Pope, forgotten minorities, old poets and young mafioso. In Exit into History: A Journey Through the New Eastern Europe (Heinemann $210), Eva Hoffman has produced a personal and poignant account of a journey in 1989 through her native Poland and four other Eastern European countries that had just undergone dramatic change - Czechoslovakia, Hungary, Bulgaria and Romania. Her journey took her through capital cities to isolated villages, shipyards, museums and the coffee houses of the intelligentsia. More travel writing, this time from Ladakh, a place almost untouched by the outside world, high on the remote Indian borders with Tibet, China and Pakistan. A Journey in Ladakh by Andrew Harvey (Picador $102) is an account of the people who live there. The diaries of British Member of Parliament Alan Clark, who served as Minister of Trade and Minister of State under Margaret Thatcher and then under John Major, are now out in paperback. Diaries (Phoenix $84) is a candid account of British political life. It is not a traditional autobiography or memoir, but a collection of notes Clark made in longhand at his desk in the House of Commons, at home, at embassies, on planes and on trains. They are exactly as they were recorded on the day, sometimes the hour or the minute of a particular sensation.