(See what I did? See how I put iTouch first and not iPhone in the title? Take that, iPhone owners! Also, my disclosure: This review is entirely my personal opinion. I have no connection with Apple or the creators of any of these apps.)
There are a lot of iTouch/iPhone apps (Ha! I did it again), and apps targeted towards knitters are no exception. So I thought I'd share the 3 apps I've found most helpful. All of these apps, once downloaded, require no Internet connection, so they're perfect for the iTouch (and you get no advantage by owning an iPhone).
1. Knit Counter Lite
This is the single most used app on my iTouch. It's basically a row counter that can hold all your projects and always saves your place. When you add a project you get a default row counter, but you can add project details to the counter such pattern info, yarn type, needle size, and any notes you want to add. You also have the option of adding more than one counter to each project. Each counter can be edited. You can add notifiers that remind you to increase or decrease on set rows, and set a limit on high the counter goes (so if you're doing a pattern that repeats every 8 rows, you set the limit to 8 and it will roll back over to 1 when you reach it). I apologize if I didn't explain this well, but it's a great app, and if you get just one knitting app, this should probably be it.
2. iKnit Needlesizer
Sure, they make those little cards with holes in them to size your needles, but do you really carry one in your purse? (I take that back...if you're anything like me, you probably do). But I bet you're much less likely to lose your iPod or phone than a piece of plastic. Using white stripes of different widths that you lay your needles against, this very basic app lets you size your knitting needles and crochet hooks in both US sizes and millimeters.
This app is basically for lazy people, but it beats carrying a ruler around with you to figure out gauge. Just lay the app on a piece of knitting, count the number of stitches between the markers on the screen, enter them in, and the app calculates your gauge.
4. Great Books (iFlow Reader)
I know, I said I was talking about 3 knitting apps, but I really want to include this non-knitting app, because it solved the great conundrum of my life: How to knit and read at the same time. The iFlow reader requires no touching to change pages or scroll the text. The text scrolls by itself; you can set the speed, or control it manually by tilting it speed up or slow down (much more intuitive than it sounds). I like to set to a little below my normal reading speed, prop it at an angle, and work on a simple project while reading the story. I suggest the Great Books library (there's a lot of book sets to pick from) because it has the widest selection of texts, including fiction, philosophy, and several other genres.