Having just got an Iphone, I am obsessed with all the different applications available. There are a whole selection of fiber related apps too. Every time I meet someone with an IPhone, I discreetly (or not so discreetly) ask to see what apps they have. Some of them are really cool, like "around me" or "urban spoon" which help you find places near you for shopping/services or restaurants. Some of them are just plain entertaining like the moron test (don't have it, played it) or paper toss (apparently very popular - don't have it either).
So here is the fruit of my research so far, starting of course with the fiber related apps:
Stitchminder- stitch/row counter
knitminder lite-project/stash/needle inventory
ewe stash-stash/needle inventory
knitgauge-really cool, has 2 slidy things that you can use to measure gauge, small ruler too
iknit ndlszr-put a needle you don't know size of on the iphone/touch and you can tell the size
yardagecalc-pick a category and yarn weight and it spits out yardage required.
I haven't fully tried out all of these, I was just really excited that there were fiber related apps. And yes, some of them are redundant to each other, like I said I was attracted by the "sparkly things".
Other apps I learned about and promised to post are (some of them cost $.99):
smacktalk-played it, very funny
shazam-here's a song and tags it artist/name of song
If you find any you love, comment back!