I have an HP NX8220 notebook with 1Gb of memory and I want to add another Gig.

The three type available are:

Kingston 1GB DDR2-533MHz PC-4200 for Notebook for $125.00

Transcend 1GB DDR2-533MHz PC-4200 for Notebook for $122.00

Corsair 1GB DDR2-533MHz PC-4200 for Notebook for $119.00

Apart from the obvious price differences which should I choose?

The existing DIMM is shown as Nanya........ According to SisSandra.

Nanya is more likely the chip maker, not the manufacturer of the SODIMM. Basically, notebooks do not have any overclocking, and so getting a quality module is not necessary. The prices seem to be fairly close, so get whatever you want.

In Thailand, the major brand is Kingston, and most shops will offer only Kingston, sometimes charging way too much for it. I usually buy Apacer, as it's usually 20-40% less and works just as well.

For desktops, there is the matter of dual-channel, where you have 4 memory slots, and need to populate two slots at a time with the same modules to get dual-channel operation. For notebooks, you also have dual-channel, but it's dual-channel in a single slot. Therefore, you don't need identical modules... which is good, since notebooks typically have only 2 slots, one of which is already populated (and some smaller ones have only 1 slot).

I have ordered the Kingston.

When it arrives tomorrow I will post again.