Let's talk apps...

[Irulan]

I've got the 16 and currently have about 9 GB of music on it... more than enough for me of everything I like. I guess it depends on how much variety you want.

[OakLeaf]

What I do on my iPod, I created a playlist based on my "eclectic mix" that only includes music with a last played date longer than 6 months ago. That way I have a playlist that's a manageable size for my 8GB iPod, and once I hear a song, it scrolls off the playlist and makes room for something I haven't heard recently. You could vary the date depending on the size of your library, the capacity of your phone and how often you listen to music.

There's also a setting now that automatically puts a lower-resolution file on your portable device. Used to be if I didn't want hi-res copies taking up space on my iPod, I had to make a lo-res duplicate on my computer and check that one to sync. No need for that any more.

[sempronialou]

You don't have to be a musician to enjoy this app. I'm totally addicted to Magic Piano. It's like guitar hero for piano, but for your iPhone or iPad.
-Bloom, Trope, and Air: They are sensory/music apps. I use them with my clients, but it's very relaxing to play with when you just need to chill.
-iFitness: It is very useful in the gym when I run out of ideas for strength training workouts.
-GPSLite: I use this to keep track of my mileage during rides and running.
-Whitenoise: It helps me fall asleep in hotels and other "strange" places.