The Mildenhall Register
The Mildenhall Register is the association for 15, 90, 149, 218 & 622 Bomber Squadrons, so this is more specific for the WWII era. For a while the site and material was not available.
This is thankfully now hosted on a new website - at www.themildenhallregister.co.uk
Link also updated on my Links page.
It has a wealth of information at this website and is a good place to try if trying to find out information or contact family members.