Blu-ray is a high definition DVD. Do you "need" one? Only you can decide that.

BTW, Blu-ray players also play regular DVD's. Many also include the ability to stream media from services like Netflix assuming you have a broadband Internet connection.

We've got a Panasonic BDP 80 that has Blu Ray capabilities, but I've never played a Blu Ray myself.
But the grandkids were here over Christmas and they rented a Blu Ray movie. I couldn't see any improvement in the picture on a 52 inch Samsung.

You have to have a hi-def TV to see the differences. We noticed immediately that the old regular DVDs looked better with our BluRay player plus the hi-def TV. More and more movies will be available in BluRay, and you can get a good player for $100 now.

You do not need a Blu-Ray DVD player, however, if you have a ten year old DVD player you will notice a difference with either a standard definition up-converting DVD player, or a Blu-Ray DVD player, which will up-convert standard definition DVDs to 720p/1080i/1080p standards through interpolation.

Your television will also up-convert the standard definition signal, and look quite good, but the DVD player can perform a better conversion while the video is still in it's original MPEG2 video format.

BTW - Quite a few of the older titles being released on Blu-Ray today are still only standard definition formats up-converted to HD formats by the studio prior to the Blu-Ray authoring of the disc - and basically using the same technology as your DVD player or television.