The corsair valuselect is pretty decent RAM actually. I have a P4 3.0Ghz system and I have 2gigs of that Corsair ram in. I was able to overclock it to 3.9Ghz using that RAM. I don't know much about Kingston though.
Damn right, one of my pc is sporting ValueSelect ram from Corsair. It's pretty stable on overclocking too. Best of all it's very affordable.
Anyways on your ram configuration. Using both Corsair and Kingston, is it same speed? Well the thing is if you're using two different ram with different speed, the mobo will automatically set both ram speeds to that of the slowest ram. So meaning, with different ram speed, its' only as fast as the slowest ram. So if the 2Gb are faster than the 1Gb then remove the 1Gb and go with the faster 2Gb ram.
Well for now, 2Gb is great for gaming. Don't see why you would need 3Gb and most of all mix the ram. Like mpjesse ask is your ram set up a 2x1Gb plus 2x512Mb on four slots? or 3x1Gb on 3 slots? It's better to have even number of ram on the slots as the odd like 1 or 3 may not operate in dual channel.
Sometimes it's better to just use the 2Gb of the same ram than mixing it with different memory modules. So you should test it and run it using the same of the 2Gb and then with the mix 3Gb and see what configuration performs the best.