I've been collecting these data bits for a couple of years now, finding gems and doing my best math to see if they fall in line with everything else. It's pretty close. Close enough to give you some useful comparisons.
2 bits: any 2 choice decision. Yes/No Run/Stop...
3 bits: A color pixel. Only 3 bits are needed to represent any colour. Red, Blue and Green, from which all other colors are derived.
8 bits: 1 byte
1 byte: Any character on your computer keyboard (not including your cat).
5 bytes: The average English word
1,024 bytes often rounded to 1,000 bytes
1 Kilobyte: A joke or a couple of paragraphs
2 Kilobytes: Typewritten page
3.2 Kilobytes: The amount of data in the H1N1 Swine Flu virus
3.5 Kilobytes: The size of the first web page
5 Kilobytes: A Desktop Icon
10 Kilobytes: A page out of an encyclopedia
17 Kilobytes: The size of an average Web Page
50 Kilobytes: A (roughly) 4 by 6 inch image
100 Kilobytes: A low-resolution photograph
750 kilobytes: The file size necessary to categorize the entire range of human experience and interest. (11 categories and about 450 unique sub-categories) as indicated by the Yahoo! directory on November 3rd 2007. (I wrote a small program to fetch all the headings and categories, save it to a text file, then view the text file size.)
1 Megabyte: Small novel, 3-1/2 inch diskette
2 Megabytes: 12 Megapixel Digital Photo, high resolution
3 Megabytes: The average mp3 song. (Rough rule of thumb: an mp3 plays about 1 megabyte per minute.)
4 Megabytes: A Non illustrated King James Bible. I downloaded a text version from Project Gutenberg and viewed the file size).
5 Megabytes: 1 minute of a YouTube High Quality video.
10 Megabytes: (Roughly) 1 minute MPEG movie.
20 Megabytes: Typical hard drive in the first desktop PCs
100 Megabytes: Roughly the text info contained in 1 meter (3 feet) of bookshelf
750 Megabytes: 1 CD. The Human genome (props to Max for his comment below)
1 Gigabyte: The bed of a pickup truck filled with paper.
7 Gigabytes: 1 DVD
10 Gigabytes: A 1 inch stack of CD's
28 Gigabytes: Tweets Per Day on Twitter as of Jan 1, 2011
30 Gigabytes: From My Life In A Terabyte - Roughly the entire collection of Gordon Bell's Gordon Bell's articles, books, correspondence (letters and email), CD's, memos, papers, photos, pictures, presentations, home movies, videotaped lectures, and voice recordings by 2003.
400 Gigabytes: 20,000 trees made into paper and printed.
500 Gigabytes: 100 DVD Movies
1 Terabyte: 1000 gigabytes
An 8 foot stack of CD's or about 150 DVD's. It would hold all 350 episodes of The Simpsons or all 238 episodes of Friends. About 2 years non stop MP3s. About 50,000 trees made into paper would be needed to print out a Terabyte of data. 250 million pages printed both sides, over 10 miles high. Roughly 250,000 MP3s (2 years non-stop listening). About 2 weeks of non-stop DVD movies. 500,000 digital camera pictures.
4 Terabytes: The YouTube record of U.S. user names and IP addresses including every record of every video watched by them as of 2008.
10 Terabytes: Enough to store everything you look at for a year, and could include a heart monitor, personal GPS, everything you type and every move of your mouse. From Charlie's Diary Shaping the Future.
45 Terabytes: All the videos on YouTube as of Aug 2006
100 Terabytes: High guess of Human brain storage space. The monthly growth of The Internet Archive in 2009. From this Google search
122 Terabytes: The size of one days Web Page views from Google in 2009 (7.2 Billion daily page views) X 17 Kilobytes (the size of the average web page).
150 Terabytes: Estimated size of all Web pages indexed by Google on Dec 8th 2005 (not including databases or video). (See this article for the figures I used)
1 Petabyte: 1 thousand Terabytes. Storage at this level signals the dawn of a new era with powerful implications to the sciences and Artificial Intelligence.
About 100 years of television. The amount of data storage space the Internet Archive had in 2004.
Roughly the amount of new video added to youTube every day in 2007
A stack of CD's 3 kilometers high
2 Petabytes: The amount of data Google processed every day in 2008
3.5 Petabytes: 2007 Estimated capacity of Google's Data centers in a box.
4 Petabytes: Estimated amount of Internet data stored in RAM by Google in 2006.
4.5 Petabytes: The capacity of The Internet Archive as of 2009. From this Google search
15 Petabytes: The amount of data the Large Hadron Collider (LHC) generates per year as of 2008.
20 Petabytes: Google daily total workload in January 2008. The storage capacity of all hard drives produced in 1995.
60 Petabytes: Estimated total size of Flickr photos by December 2011
200 Petabytes: The estimated amount of data contained within the Googleplex in 2006.
2.2 Exabytes: According to Charles Stross, all data recorded by our species in 2003
246 Exabytes: Total storage of the Internet in 2006.
1.8 Zettabytes: Estimated amount of total electronic data in existence by 2011