The best sources of current trekking information are the Kathmandu Environmental Education Project and the Himalayan Rescue Association. Both have offices in Kathmandu: KEEP is off Tridevi Marg, at Jyatha Thamel; HRA is at Dhobichaur, Lazimpath, north of the Royal Palace. HRA also maintains two rescue and information posts at Pheriche (Everest region) and Manang (Annapurna), with a seasonal post at Thorung Phedi.
These are nonprofit organizations that rely on membership dues and donations to do their work. Both have libraries of trekking-related books, logbooks full of comments from returning trekkers (invaluable for tips on routes and trekking agencies), staff who can advise on trail conditions and equipment, and notice boards for finding trekking partners and used equipment. KEEP also sells books and maps, iodine water-purification tablets and biodegradable and other trekking-related items; exhibits in the office give a primer on trekkers’ impact on the environment and culture.
It’s well worth searching the web for blogs and other specialist sources of information, too. These come and go too frequently to be safely recommended, but the best websites offer detailed online mapping, recommendations of lodges and bulletin boards where people just back from a trek share information and tips.