Essential photography filter: Cokin Graduated Filters from Test Shoot on Vimeo.

Using a graduated tobacco photography filter in Las Vegas. This example uses a Cokin P-series #197 resin filter for professional photographers and large lenses. Other photography filter brands include Tiffen, Hoya and Singh-Ray.
Even DSLRs can benefit from an actual filters on the lense that you just can't do easily in Adobe Photoshop. The best part of the resin filter is the price. They are fairly durable and cheap to replace, and since you won't use them all the time, it is not such a big deal. Singh-Ray makes expensive filters, they are a tad more durable. Tiffen also makes filters, but Cokin tends to have the most complete sets.

For the best prices, I strongly suggest Amazon shops that tie in to the big NY stores anyway, so you are better off just clicking through. To be honest, I don't get much out of the Amazon shops this so it is not for revenue, but your convenience.