There's always a new iPod in the works. Even if you bought the 5G iPod (with video) the day it came out - it's already obsolete, so who cares?
If you need/want a new iPod and the current models are a good match - buy it. If a new model comes out and you just can't live without it - sell your model on eBay/Craigslist and purchase the new model. Simple, really.