Largest (disk space) is the Classic - 160gb (also available in 80gb and 120gb). Ipod Nano comes in 8gb and 16gb form, and the iPod Touch comes in 8, 16 + 32gb. Quite why you couldn't have had a look on Apple's website is beyond me, but there you go.....

As to how many songs you can fit on an iPod, it varies heavily on many factors. Main one is bit rate - if you rip everything at 128kbps you'll get loads on there, but if you rip at 192 or 320 you'll get less.

I have 5430 songs on my 60gb iPod Video and thats over half full - Apple claim 15,000 songs can fit on one of them. However, thats based on 3-4min long songs ripped @ 128k, whereas a lot of my songs are much longer than that, and I rip @ 192k (the higher the bit rate, the better quality the sound will be. The knock-on effect however is the higher the bit rate, the larger the file size, and as such, the more disk space used)