Most major airlines can fly your personal motorcycle roundtrip between Europe or elsewhere and North America at regular airfreight prices, usually requiring that the bike be crated. However, some airlines (notably Lufthansa) fly bikes uncrated, and some specialty agents can arrange to fly your bike uncrated on the same plane you fly as a passenger, a convenient option where available. Seafreight is also available from most Euro & other global seaports to North American Eastcoast, Westcoast, & Gulfcoast ports; seafreighted bikes must usually be crated, but some companies also offer 'RO-RO' (roll on - roll off) service on ships designed for motor vehicles.

It is impossible to summarize all price & service options for shipping a bike. As a benchmark, you can usually airfreight a single bike from most Euro cities to Eastcoast US gateway airports for about $2000 roundtrip; cheaper options may be available. Roundtrip seafreight will be somewhat less, but requires a min 10 shipping days each way to & from Europe, 30 days to the Westcoast. Additional seafreight savings are possible with container-load shipments of several bikes together. It is possible for any individual to handle most of the complicated details of researching & arranging bike shipment, including Customs clearance, bike preparation, & overseas vehicle insurance; but most will want to use a local, or bike-specialist freight forwarder/agent. Some Euro & US specialists include:

Bikeworld Travel GmbH +49/(0)5231 580262, fax +49/(0)5231 580265; www.bikeworld-travel.de ; Bad Meinberger Strasse 1, D-32760 Detmold. 
Claridon Shipping (UK) Ltd: +44 (0) 1375 656100, fax +44 (0) 1375 656101; ,www.claridon.com; Claridon House, London Road, Stanford-Le-Hope, Essex GB-SS17 0JY, UK. 
Fly & Bike Reise GmbH:  +49/(0)89.66002160, fax (0)89.66 00 21 64; ,www.fly-bike.de;  Hauptstrasse 55/Rgb, D-85579 Neubiberg.
KNMV-Royal Dutch Motorcyclists Federation, Att: Jaap van Steenbergen:   +31.26.352 8520, fax +31.26.352 8522; , www.knmv.nl; P O Box 650, Zijpendaalseweg 1, NL-6800 AR Arnhem.
Knopf Motorradreisen (Stefan Knopf). +49/6221 782913, fax +49/6221 78614, German freecall 0 800 1 00 2499; , www.knopftours.com; Buergerstr 21, D-69124 Heidelberg.
Motorcycle Express (Michael Mandell). +1.516-682-9220 [US 800-245-8726], fax +1.516.682-8231; , www.motorcycleexpress.com; 6800 Jericho Turnkpike, Suite 201W, Syosset NY 11791 USA; [airfreight between NoAm & most Euro gateways, Aus, NZ,].
QCS-Quick Cargo Service GmbH. +49/(0)61 0591328, fax +49/(0)61 051866; www.quick-cargo-service.de; Kuhressenstr. 3, D-64546 Morfelden-Walldorf.
Reiseburo Buhler. +49/7431 134 300, fax +49/7431 134 3028;  ,www.bikes-travel.de;  Untere Vorstadt 5, D-72458 Albstadt.
Warren Motorcycle Transport (Warren Goodman).  +1/561-737-4954 [US 800-443-7519], fax +1/561-737-4929; , www.worldmotorcycletours.com; 10395 Utopia Circle East, Boynton Beach FL 33437 USA; [airfreight NoAm & most Euro gateways, incl. Scandinavia].