Besides the little helpers, from time to time you'll need to replace things or at least parts that are subject to wear and tear by daily use. Besides replacement blades for glass cleaners or other spare parts you'll also find suckers for filter intakes and outlets and other useful small parts.
If you want to cover your open tank with a glass cover, especially designed Cover Hooks or Cube Garden Hooks are available. They allow an optically attractive fixation of a glass cover.
Moreover, there is interesting aquascaping literature like the IAPLC Booklet (International Aquatic Plants Layout Contest Booklet) by Aqua Design Amano (ADA) Aquascaping Contest, and Liquid Magazine.
Backdrop foils for bringing some colour to the background can also be found in this category.