Programmer's Guild - We like this organization a lot. They have over 1000 members and their interests are aligned with ours to a large extent.
WashTech - the Washington Alliance of Technology Workers. They are based in Washington State and are active in IT worker issues in that state. They have a lot of knowledge of labor issues. They are neutral on the H1-B issue. Their site has news bulletins and forums. They are partially funded by the Communications Workers of America and are laying the groundwork of a union organizing campaign. They are a good source of information whether or not your interested in a union however. See comments below on the union issue.
IEEE-USA - this is a large organization of engineers that "builds careers and shapes public policy". Corporate sponsors in it's parent and affiliated organizations caused them to moderate their anti-H1B stance, which we consider the most important stance. We see this as a positive organization, it is too bad pressures have silenced them on certain issues. IEEE-USA performs an annual salary survey.
SAGE - the System Administrators Guild, currently a USENIX subgroup. You can get a copy of their year 2000 survey of sysadmin salaries (as well as other topics). SAGE had HUMRRO prepare the survey. HUMRRO is an organization founded by the US army which deals with human resources and psychology. SAGE has corporate sponsorship from companies like Microsoft, Raytheon, and Taos. It's parent, USENIX, is sponsored by Lucent, Sun, Sybase and other companies. USENIX/SAGE do not do any work or advocacy for engineers outside of the technical realm as far as we can see. It's survey of salary and other issues, as well as it's fostering of communication between engineers is a positive thing however.
ACM - the Association for Computerized Machinery is another large engineering association. They have performed salary surveys as well. They have a lobbying arm, they have not been active at all in fighting the ITAA however. They do lobby for increased government funding on scientific research, which is an interest reflective in the body of those who compose it. They also allow communication among engineers, and inform engineers of H1-B developments and the like in their newsletters.
Despite the general sentiment against unionization of our industry, old-time unions and union federations like the CWA and CESO have done some positive peripheral things that benefit IT engineers, especially with regards to fighting bad ITAA-sponsored legislation in Washington. Despite the conception that the IT industry has no unionization, there are in fact union programmers and systems administrators and so forth in some government, aerospace and telecommunications jobs. Here is a page about IT unions.