NASA: Solar System Exploration - A quality website that you'd expect from NASA, contains a wealth of information about the planets, moons and other bodies of our solar system as well mission and multimedia pages.
Wikipedia: Solar System - A huge amount of invaluable information on one page although a beginner may find it difficult to comprehend some of the language.
Nine Planets - One of the most popular and longest running astronomical websites containing an encyclopedic amount of information on the solar system.
BBC Solar System - Well designed website from the BBC in the UK, has the added benefit of containing geat video clips of astronomy based programming produced by the them.
Kids Astronomy - As the name suggests a website designed for children to learn about the solar system, very colorful with nice graphics and easily understandable information.
Space.com - A huge resource containing lots of info about the solar system and other aspects of astronomy, has a similar navigation structure to Wikipedia in that links to other pages will be contained within the text or sometimes at the bottom of the page.
Universe Today - Primarily a news website but contains a solar system page containing links to many of its solar system based articles.
Bob the Alien - A colorful and well designed website targetted towards younger astronomy enthusiasts but with lots of well written information that anyone can enjoy.
Windows to the Universe - Another huge astronomy resource with a dedicated solar system section, each page is broken down into sub sections with links on the left hand side of the page.
Enchanted Learning - A long running encyclopedic website with a solar system section, like Windows to the Universe each page is broken down into sub sections.