The official Palm Tungsten T stylii are an almost perfect replacement.
Tumnus, your talking about the ones that are spring loaded right?
Those are the ones I got. I find them to be much nicer feeling, rather solid. They also seem to be of a better quality, mine took a nose dive onto an oak floor today and survived. And the extra length from them being spring loaded is nice.
The only downside is that the original no longer 'clicks' into place. I got these as a replacement after I thought I had lost my original stylus, but later found it.
It also hangs out of the Z by a slight ammount, I took a pic for your viewing pleasure, http://www.pbase.com/george_iii/zaurus