Some study aids which I recently came across

Sing and Learn New Testament Greek (CD)

Mainly this CD puts noun endings and verb endings etc. into familiar tunes. Frequently the lyrics are not make up of words, but of endings. Well this kind of songs is not to my taste. It sounds so meaningless and awkward. I don't think I can memorize the endings like that. I prefer the endings to be rehearsed together with real words in memorable and meaningful (and fun) contexts.

Song School Greek, by Michelle Hahne

(Children's book with CD which has songs)
This is pretty cool.

Traditionally, in seminaries, we learn words which are frequent in the NT. The textbooks almost do not teach words which appear only one or two times. But in this children's book, the frequency issue is ignored. If a word is useful for real life conversation, it is taught. I like this approach. It is much more fun. I guess a student who has gone through traditional method of learning Koine Greek can try this book to help familiarize himself or herself with the rarer words in the Greek New Testament.

Mastering New Testament Greek Vocabulary Through Semantic Domains, by Mark Wilson

This is also quite cool. Words are grouped together into categories. For example, all words about clothing are listed together. All words about writing (pen, paper, inscription) are listed together. It is remarkable that the lists are often not exhaustive. For example, under the category "metal," only gold and silver are listed. Iron and copper are not. Well, this stimulates self-learning. In any case, the lists help me see that some words have the same root. I can also read synonyms together.