Need help selecting RAM

I have two P4 Systems I want to upgrade with good quality memory modules. I
would rather pay to much than to little so I am not looking to pinch pennies
in this area. I currently have installed a pair of GEMINI Dual Channel
PC2-4200 DDR2 533 sticks and want to add another pair. In looking I find
such a wide selection in a broad price range and would like some
recommendations on a good quality brand name. I also am looking for a pair
of 1 Gig sticks of PC2100(133MHz) for another System of equally good
quality. I see many posts about saving money but my main concern is quality
over cost always.

Thanks for any replies.

Cliff