OozingGoo is the largest Lava Lamp hobbyist and collector website on the internet! Many members have contributed their knowledge to make the Lava Library possible. Thank you to founder Mark Goo and the many members of the site for your collective efforts.
Lava & Glitter Lamps is one of the major Facebook groups that has also contributed greatly to making the Lava Library possible. Thank you Chase Griff for your support! This group is more focused on USA lamps, but all collectors are welcome.
The Official Lava Lamp Collectors Global is a group focused on all lava lamps world wide. Lots of collectors are in this group and upload high quality photos of their collection.
Universal Lava Lamp Lovers is another world wide focused group with most members being non USA residents. Check this group out if you want to see lots of Mathmos lava lamps as well as many other things.
Reddit has a community subreddit for collectors over at R/Lavalamps.