Pro Gun Control: http://www.americanprogress.org/
The website above is for a think tank called Centre for American Progress (CAP), which whilst describing themselves as non partisan is regarded by most to be a liberal think tank which promotes all liberal ideals, which includes strict gun control laws. They provide a section of their website to articles about guns and gun laws and all are looking at the issue from a negative perspective. Many articles show the negative impact of guns on America and look at how the government can get rid of the second Amendment. Some include promotion for anti gun activists while others talk about the weak gun law states, such as Florida, which has the 'stand your ground' law.
Anti Gun control: https://www.tsra.com/
The Texas State Rifle Association (TSRA) is an organisation that was set up in 1919 which promotes gun ownership in Texas. They support and sponsor shooting matches and teams from Texas, as well as supporting anti gun control measures. Its slogan 'Protecting Texas Gun Rights Since 1919' is a clear statement of support for gun ownership. It also proudly states it is a friend of the National Rifle Association on its homepage. Its mission statement contains three simple missions; to champion and support the rights of Texans to own and enjoy firearms; to protect and defend the inalienable rights of the individual Texan to acquire, possess, transport, carry, transfer ownership and enjoy firearms; to support junior education and rifle teams in Texas.
Both websites promote their beliefs either obviously like the TSRA website does or more subtly like CAP's does. Whilst CAP doesn't endorse political figures the TSRA has its own Political Action Committee which promotes candidates that support gun rights. However the websites wouldn't usually be viewed by people who are of opposing views to the websites, so you could argue the beliefs they promote are not likely to change minds.