We use a variant from the V-model and Spiral model to create a model for our company. We use the checks-n-balance of the V-model while using the Spiral module for risk management and developing features and enhancements in a decreasing priority manner.
The V is one thing, the iterative is another. We are looking to combine the two.
The V-model: we rather use a W-model where the one part is requirements, analysis, design, code, build, install. The quality counterpart is requirements inspections, analysis inspections, design inspections, unit testing, integration testing, system tesitng and acceptance testing.
This model should be used for each incremental iteration in the project life cycle.