Here's a useful app called Get Plain Text that lets you copy and paste plain text (no formatting) in OS X. Note that this Mac app costs $2.99 but may well be worth it's weight in gold if you have to copy and paste a lot of text from web pages.
1. Go to the Get Plain Text page in the Mac App store preview.
2. Click the View in Mac App Store button.
3. Click the $2.99 button to buy and download Get Plain Text.
"Get Plain Text is a practical utility program to process text within Mac OS: It converts copied text into plain text.
It instantly removes everything unneeded: colours, typeface size, style (for example, boldface/italics), hyper-links, images, etc. In other words, everything that isn’t plain text! Now you can put plain text in your letters and documents using the copy/paste functions, without having to clean it up manually."
Read more: CNet