Apparel and Swag

The Letterboxing Store: Silent Doug's Cafe Press store with t-shirts, hats, mugs, stickers, etc. Has "Get a Clue" shirts, "LB" stickers, and much more.
Dixie Graphix: Novel letterboxing shirts. Custom orders accepted! Lots of stickers too.
Got Clues? LB Shop: Hats, clothes, cootie buttons, and ALOT more!
Atlas Quest: Cafe Press with Hoodies, t-shirts, hats, etc.
The Sprite's Stuff: Get shirts for "Boxers n' Briefs," and Letterboxing New York, +more!
Boxing Bands: Mark&Sue have those "gel" bracelets that say "Get Out There & Box!"
Letterboxing Hats: A Son of Liberty has been making some nice hats.
Central Florida Letterboxing: a Cafe Press store with lots of t-shirts, buttons, bags, etc.
Key Fobs: letterboxing themed key fobs by Inky Squid.
Poem Magnets: a letterboxing poem on a magnet by HikerGuyEd.
Slick Kitty's Etsy Shop: letterboxing themed jewelry and journals.

Books

Letterboxing Books and Books by Letterboxers (website)

Carving and Stamping Needs

Stampeaz: The home of PZCut (now extinct) and Firm Kut! Also Mastercarve and "Pink Stuff". Lots of tools, inks, markers and more!
Dixie Graphix: She's got the "Pink Stuff," tools, ink, etc!!!
Monkey House Hobby and Home: Ink, stamps, markers, etc.
CFL Creates: carving tools an Firm Kut from Camp Fire Lady.

Journals

Monkey House Hobby and Home: Wide variety of the amazing leather Oberon journals!
Stampeaz: Moleskine, leather, sketch, etc.
Bookwright: Handmade journals on Etsy.com by letterboxer Phyto.
Gargoyle Logbooks: Handmade logbooks on Etsy.com by letterboxer Gargoyle Girl.
CFL Creates: Handmade journals and logbooks by letterboxer Camp Fire Lady. More here too.

Patches

Dixie's Patch List: A large list of letterboxing patches with links.
Mark and Sue's Patch List: Another large list of letterboxing patches with links.
The Traveling Repository of Letterboxing Patches: Complete catalog of all known patches out there by Der Mad Stamper.
Patches For Sale: Now Der Mad Stamper is also selling lots of patches to support the Travelling Repository.  Lots of old and new patches for sale.

Planter Supplies

Dixie Graphix: Lock&Locks, little containers, magnets, and much more!
Stampeaz: Journals, logbooks, magnets, etc.
First Finder Medals: metal medals for 1st finders.
CFL Creates: logbooks from Camp Fire Lady!

Stamps

Jackbear Stamps: Letterboxer Jackbear sells custom made stamps on Etsy.com.
Nitrocat: Letterboxer Nitrocat sells hand carved stamps on Etsy.com.
Pulp Art: Letterboxer Mookie sells hand carved stamps, books, and handmade papers.
DiXie: Letterboxer Dixie sells stamps, the pink stuff, cards, etc.
Sugarskull7: Letterboxer Sugarskull sells unique and custom stamps on Etsy.com.

Website Swag

Letterboxing North America: Patches, decals, Letterboxing Companion book.
Atlas Quest: Patch, calendar, Cafe Press store with apparel, mug, sticker, bag, journal, etc.
Letterpod (Letterboxing Podcast): Patch and CDs.
Boxers and Briefs: Get shirts+ for your favorite blog.