I think that some more information is needed. What will be the main usage of that machine? Do you plan to do video encoding or simply check mail and surfing the net? Or maybe mainly office software will be used in that computer? Or a media-center system?
Do you plan to use a Linux distribution or Windows? Some hardware can be a pain to be used with Linux (because of lack of drivers for example).
Can you also provide a max budget? There are so many possible combination that is rather difficult answer