Congratulations on your 30 GB iPod. I can tell you that it has changed the way I listen to music (for the better). With this many songs on here (I have 3600 right now) and the iPod on random, I'm bound to hear a lot of stuff that I haven't given a full listen to previously.
Now, for accessories. As txd mentioned, XtremeMac has some great stuff. I used to have a 20GB so I bought many of their previous accessories, such as the
car charger and the case. Their
new case looks pretty good, but check out this one:
PodPaq
I think that one looks pretty cool also.
If you drive with the iPod, you'll want some way to listen to it in your car. If your car radio doesn't have an auxiliary input, you'll need either a
cassette adapter (although you can buy these anywhere) or something like the
iTrip which will let you connect to your car radio through FM. The new model isn't out yet, but the original model got very good reviews.
Hope this helps. Good luck and enjoy your iPod! (And hang in there.)