In The Netherlands go to a “BelCompany” store and buy a “vodafone” micro-SIM card: €5, 200MB.
In Belgium go to a “Belgacom” store and buy a “Play&Surf for iPad” proximus MicroSim Card: €10, 200MB.
In England go to a “Three store” and buy an “iPad 3G micro-SIM Ready-t0-Go.”: £9.95, 1GB. Beware that many Internet Cafes have iPhone micro-SIMS but they will not authorize in an iPad.