Good question, I do see this one a lot. I have built a "few" ecommerce sites and can tell you that following SEO basics is a must. From there it is all about the product's page content. This can be a huge challenge because often times you have very similar products.
In a case of multiple colors, you want one product page with color option selection. Multiple sizes can be tricky, for clothing Amazon is a good example they list a drop down. But that may not apply to somethings like screws, piping, and in our case O-rings.
My last project I had many different sized o-rings, in many different materials, some of the different materials had the same sized o-ring. The first thing I had to do is familiarize myself with the industry. Learn why there are so many different materials, durometers (hardness), certifications and sizes. After I ingested it all and got a firm grip I moved on to a basic overview. I took a hierarchical approach. Broke the o-rings out in to material type,durometer then finally listed each size individually.
The next challenge was how to I make unique content for a same material same durometer o-ring with out risking duplicate content penalties? This is where Excel saved me. I listed out some standard information and broke out size information, everywhere possible. Then populated cells with unique information and finally in the last column did a concatenate to produce the final description. You can see an example on our site here:
By listing the sizes in metric, inch, and fractional and referencing the part number, model number as many times appropriately I was able to avoid duplicate content problems even though this o-ring description is fairly similar to the next size.
I will admit with about 8000 different o-rings this was a very long and tedious task. But thus far has proven to be a nice feather in my cap.
Another tip that I am a fan of is user reviews. Not only can you integrate a microdata schema that search engines can pick up on, but it also gives the site the ability for customers to create content for you. On the referenced site we don't use reviews but in future sites it is something I am definitely going to be implementing.
Hope this helps and if you have any follow ups on what I showed you I'd be happy to respond.
good luck,
Don