Are you going to buy another board or a new sail? Are you considering an ad in a second hand equipment market? The best thing is always to try the equipment in a rental center, before buying, or asking a friend to borrow it for a while.
Another possibility is to seek advice from one of the many windsurfing forums (forums and associations), opening a topic of discussion on the equipment you need. You can also ask for advice in Waterwind forum!
In the web, there are, however, also lots of sites that offer very accurate reviews on windsurfing equipment. You find a good selection of them in this page, so that you can get an idea of the products that you would like to buy.
If you prefer, use the custom search engine above, that will search for you through the web the tests on the equipment you need.
Finally, If you want, you can also tell us your impressions on the equipment in Waterwind special section for your review.