You know you're living in a gadget-obsessed culture when you're out shopping for stuff for the things you already have. Anyone who has a smartphone, a computer, an MP3 player, a PDA or a game console can accessorize it, thanks to an entire industry built around supplying geek gadgetry. As toys for toys go, only Barbie's overstuffed closet and Dream House can compete.

There are fewer than 48 shopping hours left in this holiday season, but for shoppers looking for a gift for the tech geek who has everything, there's plenty of time to download a stocking stuffer that every iPhone or iPod Touch owner will love: the iPhone App.

Apps, or applications created by software developers, turn the smartphone into much more than a mobile phone and music player. iPhone has thousands of apps, and the number grows daily. There are games that capitalize on the sharp graphics of the iPhone/iTouch screen, along with health, fitness, lifestyle, reference, GPS/navigation features and a growing collection of business applications. Users can even play music on their device while apps are running.

These applications are reasonably priced -- usually less than $10 -- and some are free. They can be downloaded through the iTunes Apps Store.

The most popular iPhone app download is the mobile version of a beloved computer pastime, "Sim City" ($9.99). Next is Enigmo ($1.99), a 3-D puzzle where the object is to direct streams of flowing liquids -- lava, oil and water. There are 50 levels to master and more that can be downloaded.

Bloom ($3.99) lets users go beyond listening to music and make their own. It's the creation of ambient music composer and producer Brian Eno and musician/software designer Peter Chilvers, who did the music for Spore. In play mode, touching the screen generates different notes. In listen mode, Bloom will generate music on its own.

Apps aren't all fun and games. For example, Pageonce Personal Assistant ($9.99) combines all your financial chores -- online accounts and bill payments, investments and frequent-flier miles -- into one centralized location.

Competing smart phone and handheld device-makers are launching their own versions, including Microsoft entering the fray with Seadragon Mobile, a free iPhone app. Seadragon is an image browser that enables the user to explore large collections of high-resolution images quickly and zoom in on details. It's one of the top free apps available on iTunes, where one user compared it to "using Google Earth on steroids."

Last week, Palm launched the Palm Software Store (appstore.pocketgear.com/palm), where users can download apps and software directly to their mobile phones. There are more than 5,000 applications available for both Windows Mobile and Palm OS platforms, including games (such as Tetris, Pac-man and Scrabble), productivity tools, reference materials, professional tools and more.

Before choosing an app, it's a good idea to check user reviews: Sometimes these programs have bugs, crashes and other problems.

For gadget accessories that are meant to be seen but not on a screen:

• A smartphone can be as fashionable as its owner. MP3 player and phone cases come in all shapes, sizes and prices. Every brand and model has its own collection, with polka dot and zebra stripe patterns and pop art designs. On the high end, leather and gemstone cases can cost as much or more than the device they're dressing up.

• For gamers, the Xbox 360, Nintendo and PlayStation can be personalized with an entire wardrobe of colorful face plates, along with dance pads, headsets and headphones that optimize their performance.

• Portable music players are even more fun with speaker systems and headphones to enhance the listening experience.

The Atomic Bass earphones from Radius got good reviews in PC Magazine. For $39.99, they crank out a strong bass signal, and also block out background noise. The Crystal USB Desktop Speakers from ThinkGeek ($34.99) are made of quartz crystals, which not only look cool but have natural electric properties. They work with PCs and Macs via USB connections.

• For anyone with a USB port to spare, ThinkGeek offers the USB Aromatherapy Burner ($5.99). Plug it into your USB drive, add a drop of oil, let it heat up. It comes in two flavors, rose and lavender, and can be used with other fragrance oils.

• The Speakal iPig is cute ($129), but it's also a docking station and 25-watt speaker system that works with iPods and other MP3 players, gaming consoles, computers and portable CD players.

• The iPod Pillow from KlearGear ($19.95) is several gifts in one. It works as an external speaker with an iPod, CD player or computer, and has a built-in FM radio. And you get a 16-by-9-inch pillow -- shaped like an iPod -- to boot.

• The leggy Gorilla Pod Go-Go ($29.99) from Eddie Bauer is a mini-tripod designed for the iPod touch or digital cameras.

Accompaniments like these make "toys for toys" the subplot to any toy story about multimedia entertainment.