If you have Homebrew installed (highly recommended), you can just do:
brew install id3lib
This installs several id3 command-line tools, including id3tag, id3convert, id3cp and id3info. No need for python or perl scripting; just use regular shell commands.
Usage: id3tag [OPTIONS]... [FILES]...
-h --help Print help and exit
-V --version Print version and exit
-1 --v1tag Render only the id3v1 tag (default=off)
-2 --v2tag Render only the id3v2 tag (default=off)
-aSTRING --artist=STRING Set the artist information
-ASTRING --album=STRING Set the album title information
-sSTRING --song=STRING Set the title information
-cSTRING --comment=STRING Set the comment information
-CSTRING --desc=STRING Set the comment description
-ySTRING --year=STRING Set the year
-tSTRING --track=STRING Set the track number
-TSTRING --total=STRING Set the total number of tracks
-gSHORT --genre=SHORT Set the genre
-w --warning Turn on warnings (for debugging) (default=off)
-n --notice Turn on notices (for debugging) (default=off)
Blueprint is, in my opinion, the most powerful and most useful, and comes the closest to the promise of Briefs. You get customizable standard controls, it's easy to work with, and most importantly it allows you to set up actions associated with taps, swipes, and rotation. The key is that not only can you work out a complex app interface, but you can then distribute the completed mockup so that other people can play with it using the free Blueprint Viewer app. Super, super handy.
The only downside of Blueprint, imo, is that you can't easily create mockups that don't look like a finished app. When working with outside clients or with semi-clueless management, if you present something that looks finished they'll sometimes confuse it with the idea that the app actually is close to being finished. Rougher wireframes are also useful for getting people to focus on the functionality and not how it looks. Still, a great app, the best imo.
Now to the also-rans:
Interface HD holds a lot of promise, especially the idea that it can generate some basic Xcode template stuff, but it's very unfinished and doesn't feel very polished. Definitely more promise than followthrough at this point.
UI Sketcher is designed for rough sketches and can be used for a variety of projects, not just iOS design. Unfortunately that lack of specialization means that it's not actually very good at iOS app mockups. It's so crude, really, that I've never been even slightly satisfied with a result. Maybe if I used a stylus.
iMockups and SketchyPad do have more iOS-focused controls and options, but both fall prey to the UI Sketcher problem of being designed for other things, too. Additionally neither feels sufficiently complete or polished, and everything is harder to do than I'd like. I've used iMockups to create something I actually presented to clients, but felt the need to constantly apologize for the ways the wireframes weren't quite like I intended the app to be. SketchyPad exports to Balsamiq Mockups format, so if you're already a big Balsamiq fan then it might be a good match for you. Both are definitely a step up from the looseness of UI Sketcher (or any other sketching app), but just aren't good enough to actually use for real work.
I've not used Mocking Pad, but it appears to be nearly identical to iMockups.
Best Answer
If you haven't already, check out Google Sketchup. I don't think its on iOS yet, but it is lovely in its simplicity, short learning curve and flexibility. There are tons of YouTube clips showing off features and tutorials.