Assign to your products any kind of custom field, like colors (color swatches), numbers, text and display it in multiple ways (color buttons, buttons, checkboxes, drop-down lists, etc.)
The user could build his own kit, selecting various products from predefined product groups.
A good example is a computer or a bike which consists of different parts that the user has to select
A Virtuemart search and filtering suite.
Powrefull Product Search and a Filtering module that filters with Categories, Manufacturers, Custom fields and Price range.
It is very fast and highly configurable.