Taxis/Cabs in Malé city charge a flat rate of MRF 20 (USD 1.3) for any journey. If you have suitcases, an extra MRF 5 is levied. Night charge is another MRF 5. All in all, it's pretty reasonable as a mode of transport. The only trouble is, it can be REALLY hard to just hail a cab in the city, especially on holidays. I've heard of one radio taxi service (Dial Cab Service: [960]332-3132), but haven't tried it yet.
March 1 update: Finally tried a cab service at [960]3321414 for a cab to pick me up at 6:30 AM for a flight. Total disaster - they never showed up! Will update as and when I find a reliable service.
Quick note to young women: Do NOT give your number out to just anyone in Malé. Many men will try and get your phone details, including cab drivers. Once they get your number, you will be treated to endless prank/blank calls.