Memory is getting really cheap and if you go for DDR2 667 you can get 2 GB for a mere €102. We are talking about Corsair's value select 2x1GB kit, but this memory will be enough for most people.
This is a lot of memory and for only €205 you can get 4 GB of memory. It is not the fastest and happiest solution as we are talking about DDR2 667 memory and 4x1 GB, but it will certainly do the job. You can buy it here.