I think you should cite everything that isn't yours. You don't have to provide a reference page at the end of your posts, or cite your sources like you might in a research paper (but that would be funny, so I won't stop you), but you should provide credit when it is due.
When should you do that? Allow me:
- Post inspirations; If an article, blog post, or column inspires original comment, mention that article, blog post, or column somewhere in your entry.
- Videos, photos, and miscellaneous visual material; Most videos include embed code, making it easy to post the video in your blog. Credit the creative force behind the video (even if it's just a YouTube username) and the source that provided the content to you.
Photos are a trickier situation. You should never publish a photo without permission from the photographer. (I know this goes against everything the Internet is doing.) If you see a work you want to share, contact the photographer for permission, and be sure to include the photographer's name, studio (if applicable), and a link to his or her Web site. Many artists have a blog (or Tumblr, which provides attribution for you) and have a published policy, so look for a policy before proceeding.
- Text; This should be obvious, but when you read something you want to share, make sure you list the source the text is from, the person who shared it with you, and a link to the work.
Remember, you're a journalist. You are the writer, editor, and publisher of your blog, and you have some responsibility to credit the person who published the work originally, the person who shared it with you (this may have been a personal heads up, or a blog you read on your own), and a link to the material. Those are the best ways to say thank you and provide attribution.
What is Plagiarism, and Is it Always Bad?, Consumerist