Figure 1 - People using solar viewing glasses to safely view the Sun
The transit of Venus is a rare and striking phenomenon you won't want to miss— but you must carefully follow safety procedures. Don't let the requisite warnings scare you away from witnessing this singular spectacle! You can experience the transit of Venus safely, but it is vital that you protect your eyes at all times with the proper solar filters. No matter what recommended technique you use, do not stare continuously at the Sun. Take breaks and give your eyes a rest! Do not use sunglasses: they don't offer your eyes sufficient protection.
Viewing with Protection -- Experts suggests that one widely available filter for safe solar viewing is number 14 welder's glass. It is imperative that the welding hood houses a #14 or darker filter. Do not view through any welding glass if you do not know or cannot discern its shade number. Be advised that arc welders typically use glass with a shade much less than the necessary #14. A welding glass that permits you to see the landscape is not safe. Inexpensive Eclipse Shades have special safety filters that appear similar to sunglasses, but these filters permits safe viewing. Eclipse shades are available through retailers listed at http://www.mreclipse.com/Totality/TotalityApC.html under "Solar Filters."
Telescopes with Solar Filters -- The transit of Venus is best viewed directly when magnified, which demands a telescope with a solar filter. A filtered, magnified view will clearly show the planet Venus and sunspots (http://skyandtelescope.com/observing/objects/sun/article_101_1.asp). Never look through a telescope without a solar filter on the large end of the scope. And never use small solar filters that attach to the eyepiece (as found in some older, cheaper telescopes.) See "Solar Filters" as cited above for retailers.
Pinhole projectors -- These are a safe, indirect viewing technique for observing an image of the Sun. While popular for viewing solar eclipses, pinhole projectors suffer from the same shortcomings as unmagnified views when Venus approaches the edges of the Sun. Small features like the halo around Venus will not likely be discernible. Pinhole projectors and other projection techniques are at http://solar-center.stanford.edu/observe/.
Related projection methods -- One viewing technique is to project an image of the Sun onto a white surface with a projecting telescope. http://www.skyandtelescope.com/observing/objects/sun/Solar_Projection.html and http://www.astrosociety.org/education/publications/tnl/05/stars2.html. Others follow: