Heck, why not?
1999: Spain (Algeciras) > Morocco (Tangier) > Spain (Algeciras)
2000: Estonia (Tallinn) > Finland (Helsinki)
2000: Finland (Turku) > Åland (Mariehamn)--OK, not technically international, but I'll count it!
2000: Åland (Mariehamn) > Sweden (Stockholm, or possibly Kapellskär?)
2000: France (Calais) > England (Dover)--hovercraft was cheaper than the Chunnel!
2000: Wales (Pembroke) > Ireland (Rosslare)
2000: Northern Ireland (Larne) > Scotland (Stanraer)--semi-international, again
2000: England (Dover) > France (Calais)--hovercraft again
2001: Domestic intercontinental European Turkey to Asian Turkey as mentioned above

2001: Greece (Patra) > Italy (Brindisi)
2009: Thailand (Chiang Khong) > Laos (Huay Xai) > Thailand (Chiang Khong)