I have mentioned this before on other threads, but I use a product called Preen. Using this product prevents seeds from growing into plants. It has no effect on existing plant and is no help at all with plants that spread by runners, but it stops almost all the weed seeds and stops most of the potentially invasive seeds. There are different types depending on where they are used; some include fertilizer. Between the landscape fabric, the mulch and the Preen my weeding chores are minimal. There are parts of the garden where I am allowing some things to 'grow wild' on purpose and I don't use the Preen in those areas.
http://www.preen.com/products
To save money I stock up at the end of our gardening season when items are marked with clearance prices.
