Aftermarket brands I have used and were good quality parts.
Timken Bearings: Good quality wheel bearings. If you oder AC-Delco front wheel bearings for the Imapala SS they are actually Timken bearings in AC-Delco packaging.
Where to start?

Aftermarket parts tend to vary greatly in quality and performance. With so many manufacturers in China the market is flooded with a lot of junk replacement parts out there. I tend to stick with AC-Delco parts because for the most part they have been of good quality and construction.

I have found some good aftermarket products out there and sometimes they have re-designed a replacement part to fix a weak spot in the original factory part.

When I go to the parts counter I always ask to take a look at the part before purchasing. Many times I have found that the replacement part just looks horrible and the construction does not match the OEM part at all. I know sometimes we can only buy what we can afford at the time, so sometimes it is the lesser quality part that gets purchased.

In the left column of this page I have listed some aftermarket brands that I personally have had good luck with. This is all based on my experiences and personal preference.
About Aftermarket Parts
AFTERMARKET PARTS
Precision U-Joints: This is a division of Federal-Mogul. The u-joints are of good quality.
Standard: Good quality ignition products. They also own the Borg-Warner Division (BWD) of parts
Spicer U-Joints: This is a division of Dana Corp. GM uses this brand in most cars and trucks from the factory. The u-joints are of good quality, but sometimes hard to find stocked locally.
Note: GM uses non-greasable u-joints from the factory. These joints are stronger because of lacking the cavity inside that allows grease to flow to the end caps & needle bearings. When replacing I prefer the greasable style in a car with stock horsepower, simply because it gives you the ability to grease them when servicing the rest of the chassis.
Fel-Pro Gaskets: This is a division of Federal-Mogul. The gaskets have always been of good quality and reasonably priced.