If you are looking for a plain and reliable iPhone 3G or 3GS case by a reliable case maker, I think the new Griffin Outfit (MSRP: $25) is probably a good choice that comes in two colors. This hard shell case uses the popular easy dock design (so you can pull the bottom portion out for quick docking) and has an extreme minimalist design.
The case I received is a dark gray/black that is somewhat translucent. The entire polycarbonate shell is finished with a rubber-like texture to provide maximum grip and minimal finger prints. This means the phone will stay in your pants pocket more so than not having the case on; in some cases I find the extra grip makes it a little difficult to put into my pocket. With a case like this one, you are not going to catch anyone's attention, its a utilitarian piece which is a pretty good trait. I find the case complements the my iPhone 3G nicely.
One thing you'll notice with Griffin's new packaging is that they are more environmentally friendly (paper outer box instead of plastic). I do miss, however, the cleaning cloth and screen protector film that used to come with all Griffin cases. Essentially, when you buy the new Griffin Outfit case, the case is all you get.