Remember our chat about driving and using your iPhone? Flicktunes makes controlling the iPod in your iPhone (or touch) much easier when you have to focus on other things -- like driving. Flick your finger left or right to navigate your playlist, up or down to start or stop the music. The album art is all you see, plus a speaker icon indicating playback. It's super easy, a simple app, but very useful if you're driving or otherwise occupied while jamming out.
Army Knife, $1.99
If you need to measure something in a jiffy, Army Knife is a 9-in-1 tool with several measuring tools. There's a protractor, a caliper and a tape measure, plus a level and a "heart monitor" (you tap as your heart beats). There's a unit converter with distance, volume, weight and temperature conversions, and a flashlight and whistle. The flashlight, yes, is just a screen of white, but the whistle is kind of fun and will irritate your pets (please note: I do not condone irritating your pets, please do not flame me for hating animals).
If you use Remember the Milk or Toodledoo, you should know that Todo syncs with them. There's also a free sync app for your desktop, which is essentially a backup... except there's a way to sync Todo with The Hit List via iCal. Is it optimal? No, but until THL has an iPhone app (not criticizing the developer as I'd rather it be done right than fast) this does the trick to an extent. Todo even without sync is a beautiful thing to behold and full of flexibility. In fact, the flexibility of the app is a little shocking, given the lowly status of the "to do" genre of apps. If you need a listmaker/to do/checklist app with or without sync capabilities, this is one of the best out there. Worth the $9.99 for what you get.
If you're tired of carrying around a dozen membership or discount cards, CardStar will help you out. There are templates for many retailers and discount systems (air miles and so forth), and you can choose from a variety of barcode types. I was able to experiment with the codes a bit and test things at each of my errand stops (Blockbuster, Kroger, etc.), eventually winnowing my keychain down to just 2 keys and a door opener.
I've toyed around with a few cooking apps, but if you're out and about (and have a signal) BigOven is a great way to throw a dish together based on an ingredient. BigOven basically makes everyone an Iron Chef -- at least as far as cool recipes goes. It can't help you cook things, and the text rendering could be a little more clear, but you can favorite stuff (with a BigOven free account), and copy an entire recipe for emailing. I'm not saying the interface is great, but the BigOven database is huge and stocked with what looks like good recipes.