Nike+ iPod Sport Kit - $29

The Nike+ iPod Sport Kit is the one that started it all. This tiny foot sensor for running fits in your Nike+ compatible shoe (or any other shoe with a third-party holder), calculates your distance and pace, and communicates with your iPod or iPhone, even if you're running on a treadmill. It can be a little inaccurate, so it's best coupled with the Nike+ iPhone app.

Nike+ Sportwatch - $199

Don't feel like carrying your iPhone on the run, but still want the accuracy of a GPS receiver? The Nike Sportwatch delivers everything. It comes with a Nike+ foot sensor, and uses a GPS signal powered by Tom Tom to track your distance, pace, and route, and syncs all your data to your Nike+ account online via USB.

Polar Wearlink+ Heart Rate Transmitter - $69.95

It's hard to get a proper workout without a heart rate transmitter to tell you how hard your working. The Polar Wearlink keeps it simple by linking to your Nike+ iPod setup. Beware--it doesn't work with the iPhone 4, but pairs nicely with a Nano.

Smheartlink Garmin Heart Rate Monitor - $29.99

This versatile heart rate monitor works with a variety of platforms--most importantly, the iPhone! It's also cheap and made by good ol' Garmin.

Hex Sport Watch Band - $29.95

The Hex Sport Watch Band is a stylish way to carry your Nano while running--it even has a cut out for the Nike+ transmitter, and comes in several nice colors.

Adidas MiCoach - $139.99

If supporting Nike with every step isn't your cup of tea, Adidas' MiCoach is a great alternative to the Nike+ system. Out of the box it comes with a "pacer" that coaches you on the run, a heart rate monitor, and a stride sensor. It even works with the iPhone and iPod, and you can sync your data with your Mac.

Sennheiser Adidas PMX 680i headphones with Remote Control - $69.95

This headband style set of headphones will stay put, handle sweat, and take calls during vigorous activity.

Yurbuds Performance Fit Sport Earphones - $59.95

If you prefer clip on earphones to headband style headphones, the Yurbuds Sport Earphones provide a sweat resistant solution in style.

Lobie Earbud Covers - $12

The Lobie Earbud Covers work with your Apple Earbuds for a comfortable, sporty fit. They're cheap, and come in a variety of colors.

Aquapac Waterproof Headphones - $33.27

These in-ear headphones by Aquapac are 100% waterproof, so you can swim in them as deep as 15 feet.

H2O Audio Armband - $59.99

This completely waterproof armband will keep your iPhone safe while swimming or paddling.

Waterfi iPod Shuffle Bundle - $175.99

This bundle comes with a completely waterproofed iPod shuffle in any color of your choice, waterproof headphones, and a Velcro strap to attach the shuffle to goggles.

LiveRider Cycling Computer - $99.99

The LiverRider Cycling Computer is more than just an iPhone bike mount--it's a fully functional cycling computer that wirelessly transmits to a spoke magnet on your wheel. Similar cycling computers with GPS functionality cost upwards of $300, so at $99.99, this setup is a steal!

Biologic Bike Mount - $64.99

If all you need is a tough, shock proof bike mount for your iPhone, the Biologic Bike Mount gets the job done.

SpinPower i4 Charging Kit - $79.99

The SpinPower Charging Kit provides a dynamo powered charger for your iPhone--it should be especially handy for touring cyclists that spend days on the road.

Gaiam Audio Yoga Mat - $39.95

This yoga mat has a built in speaker for your iPhone, iPad, or iPod. Play some soothing sounds with it, and you might be tempted to stay in Savasana just a little longer.

Body Media Armband - $179.95 + subscription fee

The Body Media Armband is a calorie and activity tracker that syncs with your computer and iOS device. The price, which doesn't include the regular subscription fee, is steep, but may be worth it for those who are serious about weight loss.

Gruve - $199.95

The Gruve is similar to the Body Media Armband--it's also a calorie tracker--but comes without the subscription fees. It doesn't sync with your iOS device, but it does sync with your Mac.

iHealth Blood Pressure Monitoring System - $99.95

Staying fit isn't just about working out, it's also about monitoring your health. iHealth keeps you on top of your blood pressure levels, using your iPhone or iPad.

Withings WiFi Body Scale - $159

The Withings Body Scale is a full-featured scale that syncs your fat, muscle, BMI, and weight readings with your iOS device. What else could you ask for after a hard workout?