Mobile data plan

I will be in Japan for a week. Is there a suitable prepaid mobile data plan to get? I understand there are many mobile companies and i am confuse which one to buy. Pls Help!!
Thanks

This is a commonly recommended service
http://www.bmobile.ne.jp/english/1gb.html

Depends on what you need. A sim card? A personal hotspot? A 3g/LTE modem?

Basically, what device(s) do you plan to use?

rentafonejapan.com is what I always use

I only need a SIM card with 3G. Mainly to log on to the internet to check for information while i am the. Very little of making phone calls or receiving phone calls. Thanks

In that case your options are a rental sim (data+voice but relatively expensive) or a data only option (and use a voip service like skype). Here are a few options:

http://www.globaladvancedcomm.com/simrent.html
http://www.softbank-rental.jp/e/rental-plan-ib03.php
http://jcrcorp.com/mobile/mobile_rental_simcard.htm