Useful places on the 'Net for collectable geothings.

• Pathtags (main site)
• Design a Pathtag! (Pathtag's guidance for designing pathtags)
• geocaching.com (Groundspeak's main site)
• Groundspeak's guidance (rules & costs) for producing geocoins

Other coin & Pathtag designers or producers with whom I've worked and whom I recommend.

• Geocoin.se
• bySHEERdesign Pathtags
• Atwell Family
• CoinsForAnything.com