Forums and self-reliance go hand-in-hand. In a forum you get to speak to real world people about their experiences, problems and solutions. For the most part, free of financial incentive. You can weigh up the advice you receive and move forward with a balanced overview of the issues at hand.
Here's a list of some UK based internet forums I frequent:
The Navitron Renewable Energy and Sustainability Forum: Navitron is a commercial renewable technology company, but their forum is very free form. People openly slag off Navitron products and sing the virtues of competitors products, and that's okay. Loads of stuff on renewable systems, off-grid installations and how to do it all absolutely as cheaply as possible.
BushcraftUK: The forum for all sorts of bushy folk.
Bushcraft equips you to adapt yourself to challenging natural environments in a sustainable way. A wealth of resources on living off the land while keeping warm, dry and mobile. Excellent kit reviews and an active trading section. There are definitely a few doomers on there, but they keep a lid on things for the most part.
BritishBlades: For all things sharp and pointy. As much for craftsmen and smiths as for enthusiasts.
Downsizer: for a sustainable and ethical future: A homesteading forum. Level headed folk of the earth, don't like politics much. Would rather hoe their radishes.
Ludlow Survivors Group: A British survivalist forum, yes really! Have to admit I haven't poked around here as much as I'd like. You have to stay active if you don't want your account deleted.
PowerSwitch: I did quite a
famous rant about this place back on the old LATOC board. I don't think I've ever been PM'd more on any other subject! Powerswitch is a PO board for Brits - but it tends towards doom lite.
Jack's Shed: Dedicated to countrymen ways - I recently found this place when researching the catapult thread. Looks interesting although haven't explored it thoroughly.
Airgun Forum and
Airgun BBS both do similar things in similar ways. I prefer the latter but both sites are useful.
Various car forums. This sounds obvious, probably because it is. But whatever car you drive, join the relevant forum. You can get diagnosis for head-scratchingly complex faults in about 5 minutes. These places are peopled by ex-works technicians, retired mechanics, and people who rebuild engines for fun. They want to help you. Over the years I've saved 10's of thousands of pounds by running cheap old cars with technical support from internet forums.
Bit of a specialised one here:
Song of the Paddle - Everything canoe and kayak, lots of resources on self-build
Small Woodland Owners Group for all things arboreal
Candle Power Forums for folks who are scared of the dark
EDIT: Forums added by other boardmembers - mostly SD actually! 
:DIY Doctor the clue is in the name.
DIYnot does the same thing in a similar way, but has a borderline ironic name.
ebuild.co.uk a selfbuild forum with
lots of great stuff and a very slick look.
American Preppers Network - massive resource, and they don't like apostrophes...
P2S - The British Preppers site SD linked has moved and incorporated with some other diehards to produce this forum.
modernsurvivalonline.com - not a forum, but lots of *.pdf's to download. This one should probably be incorporated into midwestherbalist's stunning
Hubbert's Arms Old Knowledge Database
