The monster success of the iPod has spawned a booming side business.

There are now dozens of third-party ear buds, in-ear plugs and head phones meant to make the sound you get from your iPod boom out better than it does with those standard Apple-white ear buds that come with the device.

Ranging from under $10 to hundreds of dollars, the offerings are so numerous that picking one can be quite confusing.

Selecting the one that works best for you is about as subjective as can be. And because theres no easy way to test them out beforehand, because of shrink-wrap and hygiene concerns, youre pretty much stuck with your choice after plunking down the money.

Youll first need to decide what type of earphone is most comfortable for you.

Ear buds are the type that come with your iPod. They just sort of sit there in the hollow of your ear, blasting out the sound through tiny little speakers.

With ear buds, depending on how loud you play your iPod, you can usually hear some of the background noise around you.

In-ear phones insert into the actual opening of your ear canal. Most come with adjustable caps to ensure a snug fit. They tend to block most outside noise.

The third type is the standard headphone that fastens around your head and rests snugly or cups around your ear.

Of seven ear devices that I have tested, I have two favorites, based on price and comfort.

Both are in-ear devices, which, since I use my iPod primarily at home, on airplanes or in the health club, tend to let me get into my own little world and appreciate the music much more than with ear buds.

My first recommendation, priced at $49, is aimed strictly for the iPod nano and comes from Apple itself. It is a pair of in-ear phones attached to a lanyard that fits around your neck and also holds the nano.

For regular iPods or the nano, my second favorite comes from Griffin Technology (www.griffintechnology.com) and is called Ear Thumps. They cost a very reasonable $19 and do a superb job of isolating outside noise. Theres a lot of bass with Ear Thumps, and you can get them in white or black.

Those are the two I recommend. Here are some others:

For ear bud users probably the best if you need to be somewhat aware of your surroundings JVC has just launched a line of brightly colored Gumy Phones. They sell for $8.50 and are widely available from electronic retailers.

With so many people buying skins and cases for their iPods in neon shades, these buds will give a color-coordinated look.

I found them to be a little more comfortable to wear than the standard buds from Apple, though it seemed to me that the Apple buds offered better sound.

There are some high-end devices worth considering if you are really the demanding iPod fanatic.

For $109 Shure Electronics (www.shurestore.com) makes the E2c Isolating Earphones.

Plugged into an iPod, they deliver the richest, fullest sound Ive ever heard. You can find them for less than $100 if you search online.

Another sound-isolating in-ear phone getting some buzz are the $39.95 RaceQuiet earphones (www.racequiet.com).

Developed for NASCAR racing fans who like to listen to scanners or radio coverage while at the noisy track, they do a great job of getting rid of background sound. I found the fidelity for music to be lacking, though.