Oh how many times i have been in this situation! However, there are ways of getting out of it, forget the waterfall model, requirements up front etc. I usually do a couple of requirements sessions with clients, this inculdes rich pictures, use case models, DFD’s, even SWOT and PEST sometimes dependign on the project, activity diagrams etc. Having done that i write my users stories WITH the client we prioritise them and start development and deliver a the project in chunks (iterations) every 2 weeks (ususally). This way i dont really worry too much if i got the requirements 100% correct, since updating and adding to the user sotires/cases is ongoing and parallel to the development. You can say that i use a mixture of methods XP/RAD/RUP/EVO etc.

Honestly, I’d like to get to know more about some of the available tools for lifecycle management..