I've just bought myself an iPod and love it. Weighs about 170g holds 30Gb of music (500-600 CDs worth) and battery lasts about 8 hours.

I haven't tried it with running/cycling etc. yet so I can't offer an opinion in that regard, but it's a beautiful piece of equipment. Excellent sound from the included headphones too.

Not waterproof etc., but there are plenty of after-market cases available for it, so you might be able to find a splashproof cover on the net.