Is your kid into Harry Potter? I'm not going to lie, this is probably the coolest thing on the list. Not that practical but presents aren't meant to be practical. Behold, the Magic Wand Remote Control. It's a wand that you use as a remote for various household gadgets (anything that uses Infrared - so most modern TVs/Stereos/Gadgets), but instead of buttons it understand gestures. Also comes in Sonic Screwdriver for Doctor Who fans.
Radio control gadgets
Everything else in the tech world may be changing, but remote controlled gadgets are still awesome.
Chances are your child has already played a game involving Mario in some way, so this radiocontrolled Mario Kart could hit the spot. Has a rechargable battery, which is a nice touch. Features fully functional directional steering and reversing. It also comes in Yoshi, a sweet dinosaur friend of Mario's.
$129 seem a little steep? Understandable. This mini version needs AAA batteries (not included), unlike the rechargeable older brother, but can still drive around fine and also comes in Yoshi.
Looking to go a bit more extreme with your radio control? You will need to shell out for express shipping this late, but this radio controlled shark is incredible. Using helium (expensive) it swims through the air as if it was water. At $82 from Fishpond with a $132 helium tank, it also comes in Nemo for only $55.
Flash drives aren't super exciting, but lots of kids need them for school these days, and they make nice stocking fillers.
Looney Tunes 4GB Flash Drive - 4GB is plenty for school stuff, and Looney Tunes is somewhat timeless. $14 from Dick Smiths, in both Speedy and Sylvestor and for a dollar more, Tweety Bird.
For eight bucks more LucasArts will endorse the present, with this cute C-3PO flash drive. Also available in Batman and Hello Kitty.
If your child already has an mp3 player of some sort - whether it be an iPod or a phone or any other brand with a standard headphone jack - speakers are a reliable choice. Cheap and fun speakers aimed at children are everywhere.
Your child has probably played Angry Birds in some way shape or form. This speaker is both cute and big enough to sound okay. Does need a plug however. $149 from Harvey Norman, also available in a pig based iPhone/ iPod version for $199.
This teensy battery powered speaker won't sound that great, but it will do the job. Good as stocking filler. $10 Dick Smith's.
A whole lot of kids electronics these days is video game based, wow. This Pac-Man battery powered speaker looks much nicer than the smiley face one, will sound better, and isn't much more expensive at $30 from Mighty Ape.
Cheaper non-apple MP3 players used to be an okay idea, but these days their prices have come down so far that iPods are a solid all around option.
Lacking an mp3 player to power those speakers? The iPod shuffle is everything a preteen needs in a music player, and they come in pretty colours. 2GB is plenty, so you can pick one up for only $64 at Harvey Norman.
For a tween or teen, the iPod touch is a much better choice - they are essentially iPhones without the phone. With wifi support, thousands of games/apps, a whole lot more music, and a beautiful retina screen, I sure would have loved one when I was 13. From $274 at Harvey Norman.