Hi Mike
there are a number of books on Tobruk, of which Morse has posted one of the best. It really depends upon what you are looking for - an "academic" history or one with memoirs/stories from veterans. here are a few more that worth a look:
Amazon.co.uk: Tobruk: The Great Siege 1941-42: William F. Buckingham: Books Amazon.co.uk: Tobruk: The Birth of a Legend (Cassell Military Paperbacks): Frank Harrison: Books Amazon.co.uk: Massacre at Tobruk (Stackpole Military History): Peter C. Smith: Books
As for the Far East, there are literally hundreds of books. If you could narrow down what it is that you are interested - maybe regiment/division, particular battle, particular force etc, we could help you narrow down the choices. For now these are excellent general histories of the Burma campaign:
Amazon.co.uk: Burma: The Longest War: The Longest War, 1941-45: Louis Allen: Books Amazon.co.uk: The Burma Road: The Epic Story of One of World War II's Most Remarkable Endeavours: Donovan Webster: Books Amazon.co.uk: Defeat into Victory: Battling Japan in Burma and India, 1942-1945: William Slim: Books
(this is probably the best memoir written by any Allied commander - completely honest and not afraid of self-criticism)