There are many many guitar string makers around the world, but here's an overview of some of the most popular:

D’Addario

"The Players Choice"
Both electric and acoustic guitar strings are supplied in sets packaged within a single 'corrosion intercept' environmentally-freindly package. Individual strings are identified by the colour of the ball-end and a key to colours is supplied on the packaging.
www.daddario.com

Dunlop

Heavy Metal Favourites
Dunlop electric guitar strings are made in California by Jim Dunlop, famous for the Cry Baby Wah-Wah pedal amonst other things. Bright, well balanced and punchy, these guitar strings are designed for extremely long life and provide low tension with minimum break-in time. Popular with Heavy Metal Artists like Zak Wylde
www.jimdunlop.com

Elixir

Hi-tech coated strings
In 1995 Elixir started experimenting with coating strings with PTFE. After much trial and error and analysis, prototypes were tried by over 5,000 guitarists and other musicians before Elixir final released their masterpieces. Today their NANOWEB and POLYWEB coated strings are used by guitar players worldwide. Not cheap to buy, but claimed to last 3-5 times longer than 'regular' strings!
www.elixirstrings.com

Ernie Ball

Probably the most famous brand of all
Ernie Ball invented the trademary 'Slinks' range of guitar strings back in the 1950s and built a world-wide brand known for it's wide choice of 'custom' gauge sets. The regular choice of millions of guitarists worldwide.
Read the Ernie Ball Biography.
>> Details of Ernie Ball Slinky range of electric guitar strings, including gauges.
www.ernieball.com

Fender

Iconic maker of the Tele and Strat
Fender invented an alternative to the ball end - the bullet end - especially for Fender guitars
www.fender.com

GHS

GHS Boomers
www.ghstrings.com

Rotosound

As British as the Beatles
Famous for ROTO Color strings (ROTO Pinks, ROTO Yellows etc) developed in conjunction with some of the worlds top artists, these unique sets deliver a smooth powerful tone that lasts while other strings have long gone dead.
www.rotosound.co.uk

....more to come!