I have used MoparPartsGiant for years and have found there prices to be lower than most and also able to get hard to find parts from them when no one else had them MoparPartsGiant
I have just today placed a order with MBPartsGiant for a CD changer for my wife's CLK 500. They had the best price MB PartsGiant

*New info as of 28 February 2025: All the "PartsGiant.com" are fronts for Auto Parts Prime, Inc of El Monte CA. There are at least 8 websites processed by Auto Parts Prime. They just process your order. Parts are acquired and often shipped from a dealership. All this is fine and often at low prices. However, should anything go astray with your order there is very poor customer service. They basically say no, find an excuse or ignore your problem. If a core charge is involved you will loose that amount, so do not purchase anything with a core charge from them. You may want to avoid them altogether.

Never hurts to check Rock Auto as they often have the least expensive price and fast shipping RockAuto
And of coarse our favorite; Needswings

This is from website Benzworld and the poster is FireFox31. It is current as of Feduary 2023.
Next time someone is asking for parts, direct them to this thread to make life simple:

This is a review of online Mercedes-Benz parts stores in an attempt to find one with fair prices for parts and shipping. Please add any stores you have used, good or bad reviews about these stores to help others, and useful details. Also, please share any buying tips you have, such as when sales are offered, how to get coupon codes, tricks for ordering hard-to-find and backordered parts, etc.

Online parts stores are divided into two categories: DIY stores and dealerships. DIY stores offer great prices and aftermarket parts (both original equipment and third parties) but only carry common parts instead of the full catalog. Dealerships offer only MB brand parts, offer the full catalog, may grant some slight discount off MSRP, but may charge high shipping rates.

For many years, I used mbpartsworld.com. They vanished at some point after I last visited in March 2021. That's a sad loss because their diagrams were great, shipping was fair, and they got me parts which other places couldn't.


NemigaParts electronic parts catalog clone - Use this to see great parts diagrams and check the part number you need for your specific build of car. Unfortunately, their data is old and doesn't include the latest versions of parts (when old bad versions are replaced). They also lack certain descriptions of parts and their prices are not current list price. MB used to offer the EPC for free but now they charge a yearly fee, so this clone is a very helpful resource.


DIY stores:
autohausAZ - Phoenix, AZ

eEuroparts - Nashville, TN

FCP Euro - Milford, CT

Pelican Parts - Harbor City, CA

Parts Geek - Doylestown, PA

RM European - Littleton, CO

ECS Tuning - Wadsworth, OH

I use and recommend FCP Euro for European car parts. Their prices and selection are great, customer service is responsive, and they ship quickly. They have a lifetime warranty on all parts they sell, replacing them for free if they break or wear out for as long as you own the car. This even works for brake pads and engine oil. To use the warranty, buy the replacement part, ship back the used part, and they'll credit you the price of the replacement. I have returned used oil and filter a few times and received the credit.

I have made smooth purchases from autohausAZ and eEuroparts but not recently enough to comment. I have always appreciated how Pelican Parts publishes how-to documents for DIY customers but I haven't used them. I'll expand this section more with your feedback.


Dealerships:
Dealership parts websites all appear essentially the same. They use the parts catalog and diagrams from Revolution Parts just like MBUSA. The difference between them is wild variation in shipping charges and slightly different percentage discount off MSRP. These sites come and go over time. A list I found here from 2019 had four sites which are gone.

To test their shipping prices, I added an oil filter and gasket to my cart and requested standard shipping to me in NH. Shipping prices did not seem to vary based on distance with AZ and MN being about the same as neighboring MA. The store location and shipping price to me is listed after each site.

Official MB USA parts - Allows in-store pickup from your local dealership.
Official Mercedes-Benz Classic parts - Great resource to see if old parts are still available.

Autohaus Parts Delivered - Peoria, IL - $10.00 shipping
Best discount (30% off) and shipping rates of all stores. Bad Google reviews.

BenzPartsHQ - Tampa, FL - $20.00 shipping

BuyMercedesPartsNow - Lake Bluff, IL - $21.00 shipping

MBDirectParts - Lincoln, NE - $17.50 shipping

MBOEMParts - $18.50 shipping
Only accepts payment through PayPal.
Reviews from BenzWorld:
Can get parts from Germany in about 10 days. Will slowly but surely fill your order. Good communication about delays.
They're a forum sponsor (still?). May have free shipping code in the vendor forum (I don't see it).

MBOnlineParts.com - NJ - $20.00 shipping
Big discounts on some parts.

MBPartsUS - Durham, NC - $18.00 shipping
Revolution Parts diagrams but Simple Part organization.

MercedesBenzPartsCenter - Hopkins, MN - $9.00 shipping

MercedesPartsCenter - $26.00 shipping
Good communication, great availability of parts. Requires VIN to process order. Can't supply backordered parts. Don't ship to Kansas or Missouri.

OEMPartsMercedes - Gilbert, AZ - $11.00 shipping
Best discount (30% off) and shipping rates of all stores. I'm considering them for my big parts orders.

ShopMBOnline - Shrewsbury, MA - $8.00 shipping
Site is a little odd.


Reviews of sellers found on BenzWorld:
Review of FCP from 2020
Review of dealerships in 2019 and 2023