One handy resource is Kana Pict-o-graphix by Michael Rowley (Stone Bridge Press, 1995).
This is a pocket-sized book (roughly 7 by 13 cm) containing just 70 pages. It contains a short introduction, followed by 55 pages with mnemonics. The top half of each page presents a mnemonic for a hiragana character; the bottom half presents a mnemonic for a katakana character. The mnemonic is simply a drawing that helps you remember the pronunciation of a character. Unlike Heisig, Rowley does not use textual mnemonics. Due to the book's small size, there are no stroke order diagrams; this may be the book's only drawback.
The last section of the book dedicates one page each to the following aspects: voiced sounds, unvoiced sounds, doublers, combined forms, and look-alikes.
There are also a number of YouTube videos with mnemonics for kana: