Listed a little while ago at over £26 now come down even more with Free First Class delivery.
Kingston ValueRAM 4GB DDR3 1066MHz Non-ECC 204pin SO-DIMM Memory Module
DDR3 is the third generation of Double Data Rate (DDR) SDRAM memory. Similar to DDR2, it is a continuing evolution of DDR memory technology that delivers higher speeds (up to 1600 MHz), lower power consumption and heat dissipation. It is an ideal memory solution for bandwidth hungry systems equipped with dual and quad core processors and the lower power consumption is a perfect match for both server and mobile platforms. Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are tied together to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.