There are two kinds of permits (Tibet visa) for traveling in Tibet: the entry permit (TTB permit) and the Alien's travel permit (PSB permit). You can get them easily from U-WayTours.

TTB Permit - Tibet Entry Permit (Tibet visa)
PSB Permit - Alien's Travel Permit
How to get the travel permits?
It's quite easy for you to get a travel permit with our help. Simply send us your information of:
- full name;
- gender;
- date of birth;
- passport number;
- nationality
And you need to tell us your occupation because journalists and people that could be involved in political matters could be revoked .You aslo need to apply for the travel permit at least 10 days prior to your entry date.
Please note that if you do not book any tour from us, we can not help you to get the permits. No travel agency can provide "permit-only" service. Here is a note from Lonely Planet:
"Lhasa PSB will not issue travel permits to individuals and will direct you to a travel agency. Agencies can arrange a travel permit to almost anywhere but only if you book a Land Cruiser, driver and a guide."
Important Issues about Tibet Travel Permit
1. All kinds of people can get Tibet permit through a travel agency except diplomats, journalists, and government officials who should travel to Tibet under the arrangement by the Foreign Affairs Office of Tibet Government.
2. With the permit, you could buy the air tickets, and check-in at the airport and the check point reroute.
3. Only our guide could hold the permitwhen you are in Tibet.You are not allowed to travel to anywhere with it wherever you want because you do need another permit named as "Aliens’ Permit". Otherwise if you are stopped by the police you will be sent out of Tibet or have trouble politically and economically. Furthermore, the travel agency which helped to get you the permit will also be in big trouble.
Therefore seriously not any legitimate travel agency could sell you the Tibet permit if you do not book a tour with them. Weare quite sure you would like to be in trouble due to a "sold" Tibet permit after you pay a lot of money for the tour.
4. There is a service charge (by the government) to get the Tibet permit. And it also takes time, paper work, transportation fee and delivery fee to get a permit for you, so TST will charge an extra fee for the permits.
Question: How much is Tibet permit?
Please note that we never SELL a permit. We only help you abtain a permit from the local authority. As mentioned above, the cost for a permit includes the charge by the government and the service fee by TST. Usually this cost is included in the quotation for a package tour.
Question: How long can I get Tibet Permit?
Generally it needs three days to get the Tibet permit if you could supply the full necessary documents. But if it needs another 3 days (or more) to Express Deliver the permit.
There is a trick that when you apply for China visa, please do not mention Tibet. otherwise you have to wait for Tibet permit and it is much easier to get the permit with the Chinese visa. In our experience seldom does TTB refuse tourists if they are not diplomat, journalist, government officials.
Other documents:
If you are coming to Lhasa from Kathmandu, you'd better get China visa from Kathmandu because no matter you've already got the visa in your country or not, you must get a visa in Kathmandu, which is regulated in an official memo between China and Nepal.