The bag I used (and still use) for my D5000 is a Tamrac 5693 (at least I'm pretty sure that's the model, I actually can't find any model number on the bag itself). It's not too big, but it can easily fit the camera with a lens attached, as well as a second lens. It also has pouches for memory cards and some other small accessories.
Here is a link (I think this it it) on
Amazon:
http://www.amazon.com/Tamrac-569304...7O7O/ref=sr_1_2?ie=UTF8&qid=1295800025&sr=8-2
It looks like it only fits the camera, but on mine there is a divided space in the main pocket for a second lens.
I actually picked mine up at
Best Buy for 19.99 last year.
There really are a ton of different bags out there, and it is one of those things that you really almost need to get it into your hands and try it before making a decision. But from personal experience I can recommend the one I have (Assuming this one in the picture is the one I have - again, be sure to get it in your hands before making a decision).
Edited - Actually after looking more closely at it, I don't think is the bag that I have, but mine looks a lot like this, but it does have more space so that you can fit a second lens. I apologize, but again, I can't find an actual model number on my bag to give the actual model. But it does look very similiar. If you go to Best Buy or a camera store it will look a lot like this, just a bit bigger.
After a bit more research I found a bag that looks more like the one I have (I think that the one I have is no longer being made, at least I can't seem to find it). This bag is very similiar, and you can see where the extre lens would go:
http://www.amazon.com/Tamrac-5562-E...2?ie=UTF8&s=electronics&qid=1295802078&sr=8-2