Normally the speakers are there to compliment the package - they don't always do this though.
If you must replace them then suggestions would be dependent on your budget.
The difference in price with / without speakers is £89 so you would have to spend a bit more than this unless going second hand.
If second hand is being considered there is a nice pair of Mordaunt Short MS20i Pearl Edition going on a well known auction site (I know Chebby rates them).
Otherwise its a list of the usual suspects that gets throw up whenever replacements for micro-system speakers is raised i.e.
Mission MX-1, Q Acoustics Q 2010, Tannoy Mercury F1 Custom, or even the new Kef Q300, B&W 686 etc etc