What is the best memory for normal working mode ?

I have 256 DDR2700 Samsung,
and work at 266 mhz
at SOLTEK DRV4,
(can not really permits overclock)

at minimal timings 2.2.2 t=1

I need to add 256 Mb,
so they can work better together,

and in future if I would want overclock,
but it is secondary and not planned still.
Just better memory for most not high price,
for perpose that I want.

What best memory for this ?

What else can be recommnded?

thanks.