There seems to be a lot of people that find their way to the forum so that they can ask for part numbers. I thought I'd put together something with the suggestion that the Mods make it a sticky.

The best on-line diagrams that give you both the Index (reference) number and the corresponding OEM part number (stock code) can be found at the Village Toyota Parts site. All of the other popular places (Conicelli Partznet, Toyota Parts Cheap) will show you the Index number and let you order the part but you'll never find the part number.

Regardless all of the sites will allow you to search for keywords. I like the Village Toyota site the best because it puts up thumbnails of all of the related diagrams that have a match for your keyword search. If you're searching for a part that has a similar name to parts used elsewhere, you can quickly identify the correct part of the vehicle from the diagrams and locate your part. I attached a couple of screen shots so you can see the differences in search results.

The other easy way to find most common parts is to get your hands on a the relevant pages from a Mitchell Collision Estimator Guide. These are thick books printed on newsprint that Mitchell puts out to help body shops estimate repairs. They are updated monthly, or near monthly, so body shops tend to have a bunch lying around. I asked my local body shop and they gave me an old one for imports for free. I just ripped out the twenty pages related to our vehicles and threw the rest of it away. You used to be able to find these easily on eBay but recently I haven't seen them.

Edit: Since I want this to be a sticky, I thought a list of sites that provide actual part numbers would be beneficial. Based on the comments, I'll add to the list. I'll only list sites that provide the actually stock (part) number.
Village Toyota Parts site
Toyota Do It Yourself - ToyoDIY
Toyota Parts Zone AKA Toyota Parts East

disclaimer: Although I mention them frequently, I have never shopped with Village Toyota. Their prices are slightly higher than Partznet and Partznet customer service is great so I normally look up the part number on Village Toyota and order from Partznet.

Attached Images

   

Thank you, it seems more and more of the sites do not want to give part numbers anymore.

toyodiy is another great plsce to get parts numbers and a sketch of the part itself.

Thanks. I decided to start a list on the top post. I included your suggestion.

I would like to offer another site that not only has great prices and service but that provides part numbers and allows you to search by your VIN #.

Toyota Parts Zone.

I usually use Village Toyota for the expanded diagrams although they seem to be unavailable for the most recent year or two.

Thanks. I added them to the list.

The best source I have found is Toyotapartseast.com. They not only have the part numbers, but the actual drawing that Toyota uses. The trademotion diagrams can sometimes be totally wrong.

Added them to the list along side Toyota Parts Zone. I thought their websites looked suspiciously similar and when I ran a WhoIs on the domains, They both came back to the same owners - Fortress Enterprise Co. It looks like Fortress owns several different car manufacturer related domains for car parts.