How to fold a Sonobe unit? Diagrams by Helena Verrill: Part 1 and Part 2. Diagrams by Dave Mitchell: Part 1 and Part 2. YouTube: Video. Very useful: Instructions for assembling various polyhedra with Sonobe units — this is a free chapter from Meenakshi Mukerji's book: Marvelous Modular Origami (2007, 92 pages).
Sonobe Variations: Sonobe3 by Meenakshi Mukerji. Two-Thirds Sonobe by Meenakshi Mukerji. Daisy Sonobe by Meenakshi Mukerji. Sonobe Variation by Victoria Babinsky.
Penultimate Module by Robert Neal: Instructions by Jim Plank.
PhiZZ Module by Tom Hull: Instructions. Another set of Instructions.
Ow's Module by Francis Ow: Instructions.
Oxi Module by Michał Kosmulski: Instructions.
An Edge Module by Carmen Sprung: Instructions.
Chrysanthemum by Leroy: Instructions.
Arabesque by Mio Tsugawa: Instructions.
Windowed Icosahedron and Snub Models by Tung Ken Lam.
Isosceles Triangle Unit by Meenakshi Mukerji.
Jitterbug Module by Tung Ken Lam: Instructions. The first step is to make equilateral triangle, which is explained nicely in this YouTube video. Models with this module are difficult to assemble because the units do not interlock snugly — you might have to glue.
Plane Sonobe: Instructions.
Many models by Mio Tsugawa.
Many models at Russian website — Kusudamas and Polyhedra.
Scanned copy of Kusudama Ball Origami (in Russian) — Instructions can still be followed.
Diagrams by Silvana Mamino — another link.
Diagrams for Three Traditional Models.
Kusudamas by Mikhail Puzakov and Ludmila Kovalenko.
Chrysanthemum by Leroy.
Kusudama Venus: Part I and Part II.
XYZ (3 Rectangles) by Francis Ow.
XYZ-mbe (3 Squares) by Nick Robinson.
XYZ (3 Rectangles) by Mick Guy.
XYZ (3 Diamonds) by Francis Ow.
WXYZ (4 Triangles) by Tung Ken Lam.
WXYZ (3 Y-Shapes) by Francis Ow.
Octahedral Cross (3 Red Crosses) by Tung Ken Lam — YouTube video
Tornado by Francis Ow.
VWXYZ (5 Red-Crosses) by Francis Ow — Photo Instructions.
Blintz Icosidodecahedron (PDF) (6 Pentagons) by Tung Ken Lam
UVWXYZ (6 5-Arm Crosses) by Meenakshi Mukerji.
UVWXYZ (6 Pentagons) by M Leonard.
TUVWXYZ by M Leonard.
TUVWXYZ (Rectangles) by Meenakshi Mukerji.
TUVWXYZ (Hexagons) by Meenakshi Mukerji.
TUVWXYZ (7 Six-Sided Stars) by Meenakshi Mukerji.
STUVWXYZ (8 Seven-Sided Stars) by Meenakshi Mukerji.
STUVWXYZ by Meenakshi Mukerji.
STUVWXYZ by Meenakshi Mukerji.
RSTUVWXYZ by Meenakshi Mukerji (Photographic instructions).
RSTUVWXYZ by Meenakshi Mukerji.
RSTUVWXYZ by M Leonard.
QRSTUVWXYZ by Meenakshi Mukerji.
Four Intersecting Tetrahedra: Instructions by Tom Hull. YouTube: Video Instrucions.
Six Intersecting Squares by Robert Lang: Instructions by Jorge C Lucero.
Robert Lang's models (called Polypolyhedra): Part 1, Part 2 and Part 3. To visualize these models, VRML models by Carlos Furuti are helpful.
Daniel Kwan has uploaded Pictures and Instructions at Flickr. Since these are challenging to navigate, I have sorted individual models for you:
Four Triangular Prisms: Picture and Instructions: Part-1, Part-2, Part-3 & Part-4.
(Starburst) Six Pentagonal Prisms: Picture and Instructions: Part-1, Part-2 & Part-3.
Three Square Anti-Prisms: Picture and Instructions.
Five Truncated Tetrahedra: Picture — Instructions not available.
Four Irregular Hexahedra: Picture and Instructions.
Five Wrinkled Octahedra: Picture — Instructions not available.
Three Gyroelongated Square Dipyramids: Picture — Instructions not available.
Quadra-hadra-pudra-phedron: Picture and Instructions.
Dice by David Petty.
Fuzzy Cube by David Petty.
Knobbly Cube by David Petty.
Menger's Sponge by David Petty.
Umulius Rectangulum by Thoki Yenn: Instructions and Instructions. YouTube videos: First and Second.
Tri-Module by Nick Robinson (for fractals): Instructions.
Spike Balls by Rona Gurkewitz and Bennett Arnstein.
Stellated Dodecahedra by Paolo Bascetta.
Ostrum by Tchami.
Lazy Tetrahedron I by Tung Ken Lam.
Lazy Tetrahedron II by Tung Ken Lam.
Sprinklers by Paula Vernick.
Bucky Balls by David Petty.
That Simple Unit by Charles Esseltine.
Butterfly Ball by Kawamura: Part I — Part II — Part III.
Curler Units by Herman van Goubergen.
Football by M Leonard: Part I — Part II — Part III.
Icosahedron by M Leonard.
Diagrams by Maarten van Gelder (check out Star Kusudama).
Meenakshi Mukerji &dmash; Mio Tsugawa — Francis Ow (I & II) — Jorge C Lucero — Silvana Mamino (Diagrams) — Mikhail Puzakov & Ludmila Kovalenko — Dave Mitchell — Michał Kosmulski — Nick Robinson — Robert Lang — David Petty — Mark Leonard
latrenza.wordpress.com has Diagrams — Modular Ball by Fumiyaki Kawahata and Web Star by Philip Shen.
Origami Kawakami at Brazil has lots of pictures and instructions.
Jorge C Lucero maintains orig4mi.wordpress.com.
origami-modular.blogspot.com has instructions.
diagramascia.blogspot.com by Isa Klein has diagrams.
Portugese website — Modular Origami has Photo Instructions for many models.
Modular Origami in Argentina by Laura Azcoaga — Plane Sonobe and Scaled Octahedron, for example.
Two diagrams by Ingeborg de Wolff: Step by Step 60 and Kusudama.
Free Diagrams by Oriland (Yuri and Katrin Shumakov).
Centro Diffusione Origami: An Italian website with a couple of free diagrams.
A Mexican website with a couple of free diagrams.
3-D stars with strips of paper.
Ingeborg de Wolff has made models from numerous books! A gallery with links to diagrams
OrigamiNut.com — several video instructions.
Meenakshi Mukerji — with links to diagrams.
Gurmeet Singh Manku — with links to diagrams.
Halina Narloch — Gallery — with links to diagrams.