If you are serious about learning a language, it’s worth going to the trouble of equipping yourself with a set of resources that will not only stand you in good stead over the long haul but will also be a pleasure to work with. In essence, you’re choosing life-long friends with which to share your life, so you can afford to be demanding.
Here I offer some reviews of resources I have found useful. The editions mentioned here are the ones I have; they may have been superseded or not be available at all. In any event, I hope that the points considered here may guide you in your own selection.
My strong advice is, if at all possible, to see representative pages of any book before purchasing it. This applies to works of fiction as much as to textbooks of any sort. You want to judge whether the content, layout and typefaces meet your needs and suit your taste. This is particularly important in the case of dictionaries bought over the Internet. All too rarely, publishers and online booksellers afford prospective customers the opportunity to view sample pages. Even when they do, it is amazing how often such pages are confined to introductory material which is hardly representative of the bulk of the product. In essence, you are expected to act counter to the old saw and judge a book by its cover. It would not hurt these organizations to show people even a single representative two-page spread of a book. The risk of plagiarism would be very low and should be more than offset by increased willingness of customers to purchase. If necessary, contact the publisher, suggest this as a general practice, and request an image of such a representative spread.
Unless otherwise stated, software and apps mentioned here relate to Apple operating systems only. This is not to say that versions of them for other operating systems aren’t available. Be aware that not all iOS apps work the same (if at all) on all iOS devices: my experience of iOS apps is on an iPhone only. Always check the hardware and system requirements for any software before purchasing.
Don’t overlook older books such as you might find in secondhand bookshops. You might find a useful list or table, or perhaps a helpful mnemonic. Always worth a quick flick through.