ThoughtWorks had a very thorough interview process that spanned a number of days. It was slightly frustrating because one had to take out between 1 and 2 hours over 3 days or go in and spend a whole day with them (choice is yours)... but I appreciated and respected the thoroughness of the process.
Initial Phone interview with HR: went on for over 45 mins. The interviewer asks you questions designed to test your thought process and makes notes of your answers. Some of the questions are definitely off the beaten part E.g. what do you think of the future of facebook? There was also an opportunity to ask after the culture of the company and other questions that the candidate might have.
Testing: Two tests that took about 20-30 mins each. They call you in to their premises. For a BA role, the tests were (i) general aptitutde and (ii) comprehension (if i remember correctly)
Panel Interview: An interview with two contemporary BAs. We did a role play session where they played stakeholders and put me in a mock requirements gathering situation. I storyboarded stuff on a pencil and paper. It seemed to go down well with them. You can also ask them questions about the work culture, why they like the place etc.
1:1 Interview: I don't remember who this was with but it was with someone high up. This is just an opportunity to clear out the final details: he'll ask you what your career plan is, why you think you'll fit in well etc. You can ask him what sort of growth you can expect etc.