NRA competitive shooting programs is a great reference for the many different shooting disciplines and a great organization to be a part of.
The Encyclopedia of Bullseye Pistol is an incredible source of information regarding bullseye pistol shooting. On this site you will find written articles regarding shooting technique & shooting psychology, technical information, tools of the trade and much more.
Pistol Shooting by Allan Lozsan is a site which provides some useful information regarding shooting technique, strength & stability, grip modification and a few other subjects that may help raise those scores.
Troy Lawton is one of the very best offhand shooters on this planet. He’s competed in rifle silhouette and running target and has national records and championships in each event.
Boy Scouts of America
National Shooting Sports Manual
If you’re a Boy Scout working toward your Rifle Shooting Badge, this resource will help if you’ve chosen option B of the requirements.