The Republican proposal would divide illegal immigrants into three categories:

Those who had been in the country the longest, more than five years, would not be required to return to their home country before gaining legal status. They would be subject to several tests, including the payment of fines and back taxes, and be required to submit to a background check, according to these officials.

Illegal immigrants in the United States less than five years but more than two would be required to go to a border point of entry, briefly leave and then be readmitted to the United States. As with the longer-term illegal immigrants, other steps would be required for re-entry, after which they could begin seeking citizenship, these officials said.

Illegal immigrants in the United States less than two years would be required to leave the country and join any other foreign residents seeking legal entry.

Under the Senate Proposal, called the Chairman's Mark, includes a legalization provision:

Undocumented immigrants who were working in the U.S. on January 7, 2004 could qualify for temporary lawful status for 6 years if they pay a $1,000 fine and fees, have complied with tax filing requirements, have not committed certain crimes, and understand or are studying English, U.S. civics and history. After the 6-year period, applicants who have worked or studied continuously and meet the other requirements of the bill would be able to adjust to lawful permanent resident (LPR) status after payment of a second $1,000 fine and additional application fees.

It also includes a guest worker program:

Foreign workers would be allowed to enter the U.S. and fill available jobs that require few or no skills so long as the applicant demonstrates that he/she has a job waiting in the U.S., pays a $500 fee and application fees and meets security, medical and other conditions. The guest worker visa would be valid for three (3) years, the visa can be renewed for an additional three years, and after four years the worker could apply to adjust his/her status to LPR status.

There's a special provision for agricultural workers:

It would allow undocumented farmworkers who worked in agriculture at least 150 days within the previous two years before December 31, 2005 to apply for a "blue card." If they work an additional 150 work days per year for 3 years, or 100 work days per year for five years, they can apply for lawful permanent resident status. They must pay a fine of $500, show they are current on their taxes, and that they have not been convicted of certain crimes. They can also do non-agricultural work during this period.

There would be a reduction in immigration visa backlogs:

Immediate relatives (spouses, children and parents) of U.S. citizens would no longer be counted against the worldwide limit of available visas, and those visas would be made available for other family categories. The number of visas for employment-based visas would be more than doubled. The children and spouse of a U.S. citizen who have applied for an immigrant visa would be allowed to continue with their application if the citizen dies before the visa is issued.

It also contains the Dream Act:

Also included in the bill is the DREAM Act (S. 2075), which would allow immigrant students who have grown up in the U.S., graduated from high school here, and can demonstrate good moral character to initially qualify for "conditional lawful permanent resident" status, which normally would last for six years. During the conditional period, the immigrant would be required to graduate from a 2-year college, attend 2 years towards a 4-year degree, or serve for 2 years in the military. At the end of the conditional period, those who meet at least one of these requirements would be eligible to adjust to LPR status and could apply for citizenship without any further delay. The bill would also eliminate a federal provision that discourages states from providing in-state tuition without regard to immigration status.

There are still a long list of punitive provisions in the Chairman's Mark bill. But, some modifications were made that make it better than 4437, including:

• The provision making unlawful presence a misdemeanor was removed.
• The humanitarian exception to the provisions making assistance to immigrants a crime of smuggling was broadened to cover non-emergency medical care, counseling, victim services and housing.
• Some of the retroactive application of punitive provisions was eliminated.
• Limited judicial review of naturalization decisions and delays under current law was retained
• Refugees, asylees, and certain vulnerable populations would have limited protection from prosecution for the wide range of document fraud provisions.
  
  Still up in the air is the appeals provision:

Title VII of the Specter mark, which would limit all immigration appeals to the Federal Circuit Court of Appeals, and permit such appeals to proceed only in cases where a judge issues a certificate of reviewability within 60 days, in effect preventing most immigrants from appealing adverse immigration decisions. This title was pulled from the bill by Sen. Specter. A hearing on the issue will be held in the Judiciary Committee on April 3, and some version of the provision is expected to be offered as an amendment on the Senate floor.

Here's another good analysis, with links to all of the actual bills (except the one proposed late Wednesday).