By far the best Indonesian-English dictionary is A Comprehensive Indonesian-English Dictionary: 2nd Edition by Alan M. Stevens & A. Schmidgall-Tellings (Editors). However, it is quite expensive. A cheaper option, but still good, is Kamus Indonesia-Inggris: An Indonesian-English Dictionary by Hassan Shadily. There is also an English-Indonesuian dictionary from the same author. Both are very good. Then there is the equally good Indonesian-English The Learner’s Dictionary of Today’s Indonesian by George Quinn. These are the only ones that we can recommend at the moment.
When you are a little more advanced, download the free application of the Kamus Besar Bahasa Indonesia. This is a monolingual dictionary, and the official dictionary of the Indonesian language. An excellent choice once you’re a little more advanced. Instead of the application you can also use the KBBI website
There are many grammars and all have their pros and cons. The one that we use all the time is the Indonesian Reference Grammar by James Neil Sneddon. The same author also published The Indonesian Language: Its History and Role in Modern Society.
Users of «The Indonesian Way» do not need to purchase a grammar (although we still recommend it), but once you progress to the higher level courses such as «Aneka Baca», «Baca Yuk», «Serba-Serbi Nusantara», «Ada Apa dengan Cinta», or «Anak Jalanan», we strongly suggest that all students purchase and make frequent use of Sneddon’s grammar.
The only one that we can recommend with caution (it contains a few mistakes) is Indodic (free).
Comparison of Indonesian with other Austronesian languages:
As you can see, Malay, including its Indonesian and Malaysian variants, has a lot in common with other Austronesian languages as far away as Madagascar (Malagasy), or New Zealand (Maori). Given that East Timor is an enclave within Indonesia, it is not surprising that its national Language Tetum also has a lot in common with the Indonesian-Malay language.