I've previously written about lists and reviews of remote testing tools, but this article by Nate Bolt probably does the best job of providing well structured context too.
Nate - author of a great book on the subject - classifies tools under:
- Method #1: if you like people
- Method #2: if you like machines better than people
- Method #3: if you like people, just not talking with them
So if you're new to this kind of thing, thinking about yourself is probably as good a way as any to decide which tool or method you might pursue.
The article is a couple of years old now, but I think the range of approaches and why you might consider them still holds good. There will of course be even more tools to choose from, doing more sophisticated things by now.
Quick and Dirty Remote User Testing - article by Nate Bolt for A List Apart
Remote user testing advice from Nate Bolt (August 2010)