Firefox: DeSopa is the latest Firefox add-on that can counter the Stop Online Piracy Act (SOPA)'s DNS blocking if the bill passes. The extension gets you through sites censored by DNS and lets you browse them by IP address
To use the extension, you just need to click the DeSopa button to switch to accessing sites by their IP addresses. Click again to go back to standard DNS resolution.

Some sites may not be directly accessible by IP because they're on virtual hosts, and DeSopa also doesn't resolve subdomains. If you can't get through with DeSopa, previously mentioned The Pirate Bay Dancing from MAFFIAFire should do the trick.

Developer T Rizk offers this add-on as proof of concept that SOPA will not help prevent privacy and will only do major harm:

The program, implemented as a Firefox extension, simply contacts offshore domain name resolution services to obtain the IP address for any desired website, and accesses those websites directly via IP. Similar offshore resolution services will eventually maintain their own cache of websites, without blacklisting, in order to meet the demand created by SOPA.

If SOPA is implemented, thousands of similar and more innovative programs and services will sprout up to provide access to the websites that people frequent. SOPA is a mistake. It does not even technically help solve the underlying problem, as this software illustrates. What it will do is give undue leverage to predatory organizations, cripple innocent third party websites, severely dampen digital innovation and negatively impact the integrity and security of the Internet.

It's questionable whether this extension or others like it will help Congress members "err on the side of reason and vote SOPA down" as T Rizk hopes, but at least we have countermeasures if the bill passes.