We already have many guest worker programs in the form of various visas such as H1B, H2B, TN Nafta Work visa, L-1 Intra-company Transfer Work visa, Nurse Work visa, O-1 Visa, P Visa, R-1 visa, etc. There are millions of people working here as guest workers under those programs.
Here are current classifications of Visas (There may be other special classifications, e. g., military personnel from other countries training in the USA):
Employment Visas
H-1B
H-2A
H-2B
H-3
O-1
Business Visas
L-1
I
E-1
E-2
Education Visas
J-1
H-3
M-1
F-1
Fiancee - Marriage
K-1
K-3
Other Visa Categories
B-1(travel-biz travel)
B-2 (travel-biz travel)
C (transit)
D (vessel crew)
R (religious)
Student Visas
Academic F-1 Visa
Non-Academic M-1 Visa
Requirements for general travel visas (like vacations) vary by country of origin. For Canada and Mexico, at least thru the end of this year, no passport is required to visit the US; all that is required is a valid country issued ID with a photograph. A new law goes into effect on Jan. 1, 2008, which will require all citizens of countries in North America to have passports when visiting the USA.