There are lots of options out there:
1) Mtx Connect (a sim card that is data only and works in a lot of countries, with different data packages or a 4 cents/MB rate)
2) Travelsim/Lemonsim/Airbalticcard (the latter in particular offers several data packages)
3) Piranha Mobile (no data packages but interesting pay as you go rates and two mobile numbers, US and UK on the same sim card).
I believe those listed above are the best options you can get, instead of spending lots of money using international renting services. By using what I suggested you can get both a worldwide valid phone number plus data traffic.
Hope it helps.
Ps. here in Europe since June 15 roaming costs will be erased in case you have a monthly package, even prepaid, but those sim international roaming cards remain valid if you don't want to get entangled in a monthly plan.