weber.com has good information. But here is a summary:
There are three "trim" levels: Silver, Gold and Platinum. And for each, there's a B and C model - C has a side burner, B does not. (There's also a Silver A - the only "A" model - which is a 2-burner grill. All the others are 3 burner.) Also, the Silver B has a "narrow" cart... the Silver C and all the Gold's and Platinum's have a wider cart. Look at weber.com and you'll see what I mean.
For the "base" grills as listed on weber.com:
- Silver models have a black (or colored?) hood, porcelain-coated steel grates and flavor bars.
- Gold models have a stainless hood, grates and flavor bars, and add a swing-up shelf on the right side.
- Platinum's also have an all-stainless frame and stainless inserts in the shelf surfaces.
And to confuse things further, exactly what you get can vary depending on where you buy. Home Depot includes the porcelain coated cast-iron grates, and there's also a "specialty retailer" setup which includes solid stainless grates and a few other upgrades.
It's confusing.