How many GB's in a memory card does a Nikon D5000 need?

I know it depends on how many photos I want
but how many GB's in a memory card do I need
for excellent, clear, and can stock up to many photos?
I need help

The only thing that is effected by the GB's of the card is how many pictures you can store on the card. But you need to check your manual and get the right type (SD, Mini SD, XD, ect.) and some, not all, can't write onto super large cards (mine won't write on cards above 12 GB).

I agree. The size of the card, and don't forget its speed, has nothing to do with quality of photos.
That's up to you and the camera.

What the speed does, I use Class 10 cards, is allows faster shooting because of the write speed that helps the data flow faster through the camera's processor.

Get 8gb, it's affordable, holds a lot of pics and video and if you lose it you won't lose too much in one go. A D5000 takes SD. Class 6 or better will be just fine.

First, you do NOT want to stock up photos on your SD card. The more photos it holds, the less likely you are to transfer them to a computer- which is much safer than the SD card.

if you are going to focus on picture taking over video, then I suggest a couple 4gb class 6 SD cards at the very least.

if you are going to do video, a couple 8gb or 16gb class 10 SD cards are needed.

I use a 4gb class 6 in my Nikon D40 and I have no trouble

You should go with BLAZING 16GB SDHC Class 6

16 GB storage capacity -Class 6 - Guaranteed fast data transfer minimun rate 6 MB/ seconds for reliable copy/download/backup.
Usable with an extremely wide range of devices that have Secure Digital compatible w/ media slots.
Low battery consumption to maximize battery life in small portable devices.
User-selectable mechanical write protect switch on the exterior card casing.
** 3 YEAR WARRANTY **