cozit83, from your previous post you take a lot of seascapes and are having trouble with exposure. Exposing for the foreground in this situation will likely leave the sky over exposed, exposing for the sky will likely leave the foreground under exposed. The traditional way to correct for this is to use a Graduated ND. Check out this link for an explanation of what they do and how to use them
http://www.amateurphotographer.co.uk...ensity-filters
There are several reputable brands to choose from, it really comes down to your budget. The square type filter with associated filter holders are the best system, as these allow you to position the filter accuratly to get the effect you desire. Brands such as Kood, Cokin and Lee all manufacture this type of filter, to suit a variety of budgets. IMHO Lee are the best but they are expensive. I've also used Cokin in the past and they are much more affordable.