The greatest thing since sliced bread…
Of course, I have to include my favourite plugin provider – Itoo Software. Their plugins Railclone and Forest Pack are the best tools out there for parametric modelling and scattering – and any other use you can think of. To date, I have modelled a building entirely with railclone, created traffic setups, added curtains to buildings, interior furniture setups, made a fruit bowl, made a commercial doormat.. and of course, I use it for almost every situation where I need vegetation.
The support is one of the things that makes them so good – they are always adding new features, and are very responsive to bug reports and user questions.