These are websites which you can generally start writing for right away.
Basic - Simple submissions policies with simple content requirements.
Intermediate - Simple submissions policies, although having interest, knowledge, or background in a particular niche/topic may be necessary.
College Humor is a comedy/entertainment website which will accept comedy/entertainment oriented articles. They offer fixed payments dpeending on the length of your articles.
Curbly is a DIY community with emphasis placed on home improvement and interior design. It is possible to negotiate your compensation for articles you submit.
Redgate Hub is a community centered around IT and technical professionals. They accept materials oriented towards computer/technology topics such as programming and IT work.
SitePoint is a web design hub and a publisher of materials centered on web design. Every month, SitePoint publishes a hub in which a topic is chosen by the editors and is then made available for open contributions.
The Diplomat is a current events journal with emphasis placed on the Asia/Pacific Region. They accept articles and blog posts based on economics, environment, politics, etc. You can have compensation arranged for your submissions arranged in advance with the editor.
Travelista is a travel blog which will pay up to $40 for articles related to travel or even travel documentation about the area in which you live.
Advanced - Websites which require credential, educational, or background checks before you can begin writing for them. They often prefer already established freelance writers.
Special - Unconventional content requirements.
The Hallmark Channel is a special case, as it has a substantial submission requirement. They are open to mystery, drama, and romance novels 60,000+ words in length. They are also not specific about how you could be compensated for an accepted submission, albeit their position as a television network could lead to potential publicity around your work.
A website which will allow you to publish and place royalties on books or other extensive materials you have written on a variety of more technically oriented topics (Programming, DIY, Art, etc).
The Smithsonian Magazine is open to article submissions covering topics ranging from science, history, arts, and more. They prefer already estbalished freelance writers and they have immediate credential checks on their application page.