Service availability, size/weight limits, and cost vary by country, but here's a general rundown.

DHL - 3-10 days transit times. Cost is based on volume (primarily).  No size limit.  Voids in the shipping box can be filled (within reason) without incurring extra shipping charges (i.e. headlights packed in the arch of the bumper, etc). 
--Method generally used for wheels, bucket seats, bumpers, trunk lids, lip spoilers, etc.

EMS - 5-10 days transit times. Cost is based on weight with smaller size limits than DHL.  1.5m length limit AND length + circumference has to be less that 2.75 or 3m total (varies by country).  Weight limit of 30kg (some countries 20kg).  The EMS Rate Chart can be found here so you can get an idea for yourself: EMS RATE CHART 
--Method gernerally used for large lightweight items like lights, steering wheels, interior panels, trim, etc.

SURFACE MAIL - 2-3+ months transit times (varies by country). The same or smaller size and weight restrictions than EMS, but the cheapest option overall.  Service is operated by JP Post (same as EMS).  Insurance unavailabe to some countries.
--Method generally used for wheels when saving money is more important than speed.

--Reclinable semi-bucket seats can be separated top and bottom
--FRP aero can be cut and packaged much smaller
--LSD's removed from differential housings and cleaned
--OEM front/rear lips folded/bent to fit EMS size limits
--Please inquire with your custom request

For more details, see the Process Details page, but just note the additional service fee will be far cheaper than the unaltered shipping cost.

Items that cannot be shipped:
--New or used coilovers (currently)
--Used fuel injectors, fuel pumps, etc.
--Anything excessively greasy/oily that cannot be cleaned prior to shipping