Travels

Best place I've found so far to look for flights and accommodations abroad:

Despegar.com

Travelling? 2

Local Travel agencies' sites. Most are useless, but at least include contact information.

Transatlántica Viajes y Turismo
Casting Travel Service
Daminato Viajes y Cambio SA
Freeway - Operador Mayorista de Turismo
Romer
Turismo Stoisa
KAUMA Tour
Viaja-YA

Travelling?

Planning a "Grand Not-Really-a-Tour" (meaning international, really expensive travel), I'm considering two destinies first (hopefully): the United Kingdom or Japan. Most logical place to start: London. With that in mind, some places to check:

UK in general
VisitBritain.com - Britain's Official Travel & Tourism Guide! Plan your UK Holiday Now! (scores of information, including London)
Tourist Information UK - Your Guide to England, Scotland and Wales

London in particular
London's Hot-Map - interactive map (page is in German)
Transport for London - Getting Around - maps and timetables for the tube, buses, etc. (includes interactive maps, like this one for the tube)