Grumpy Mac is right and wrong. Blu-ray players do a credible job of upscaling DVD and therefore improving the DVD image relative to a standard DVD player. They can't give you "real" HD. While upscaled DVD images are technically HD they can't contain all the information in a real HD image like Blu-ray.
That said, there are lot's of considerations to take into account before deciding to buy a Blu-ray player.
First, if you are going to continue to watch DVDs (and not buy or rent Blu-ray disks) you don't need a Blu-ray player ... you need an upscaling DVD player (it's about 1/3 the cost of a Blu-ray player).
Second, Blu-ray disks require a minimum moderate sized 1080p HDTV (e.g. 37" or larger) to provide maximum benefit. There is no advantage to Blu-ray (or an upscaling DVD player) on a standard TV.
Third, Blu-ray disks offer superior sound to DVDs because of advanced audio formats. ... but you must have a good audio system to hear the difference.
Fourth, Blu-ray disks are, and will remain, more expensive than DVDs. They are a premium priced (and performance) DVD alternative.
Fifth, unless you watch close enough to see the difference (many HDTV viewers sitt too far from the screen), Blu-ray won't look much better than DVD.
So ... a Blu-ray player is a good bet if you are comfortable paying extra for Blu-ray disks and intend to slowly switch to Blu-ray, but if you intend to stick to DVDs consider an upscaling DVD player instead. Just recognize that any improvement won't be startling.