As part of their recent network upgrade to LTE, Roam Mobility has spiced up their plans. The new Text+data plan is an interesting option for people who don't really use their smartphone for calling (which is a surprisingly high number).
Now my caveat. Anytime you see unlimited data, it is on the T-Mobile 2G network which is painfully slow and has spotty coverage across the US. It is enough to [very slowly] download emails but, during my tests in New York and Vermont, it was too slow for GPS navigation or web browsing on my iPhone 5s using Safari or Chrome.
The new LTE network seems to be blazing fast and I will test it during my upcoming trip to Los Angeles (expect a blog post early September).
For Canadians travelling to the US, Roam Mobility offers the best price/value options. Their Data only plans are incredible values. As an example Rogers charges 8$ per day for 50MB. Roam gives you 300MB (valid for 3 days) at 8$.
Source: Roam Mobility