For flight clearance, use this link: http://www.thaiflyingclub.com/linkflightclearance.html
Refer to this link for Thailand ENR with VFR area charts, Aerodrome directory (samples below) and PTT Fueling sites etc: http://www.hebels.nl/flights/thailand/index.htm This data has been complied in 2007 and is unauthorised, not updated and maybe in error.. but its a good starting point!
Some of the best information can be obtained from the Thai Flying Club website.
Thai DCA AIP is, at time of writing, not working.