you can try ableshoppers.com or slickdeals.net for some rebates. Also, you can go to the refurb section in the online Apple store, sometimes you can get lucky.
Mini/20GB/40GB/Shuffle, depends on what you're using it for. I've amassed an iTunes library of existing/old MP3s and iTunes purchases that is about 31GB, but doesn't include all my CDs. But I don't keep all of it on my 20GB 4th gen iPod. I just manually sync certain playlists so that I can manage the size.
Mini - good if you want a small package, maybe if you want it for active exercise. Shuffle is probably better for this but it's only up to 1GB.
Photos - good if you want a BIG HD and you want to show pix.
20GB/40GB/etc - works best for me. Small enough form factor and large enough drive.
I bought one for my father in law for xmas and ended up getting an extra for myself. Used a friend of family 10% coupon at CompUSA.
I also have a toddler who likes her music in the car. So I burned all her CDs and created a playlist of her favorite songs. Now I don't have to keep hitting skip on the car CD player. But I do have to listen to her music...
I also got audible audiobooks for my commute to work.
I love my iPod so much I bought a Mac Mini to go into my Home Theatre. It's being set up to support iTunes instead of my PC.
