The first one I ever used on my blog was ClustrMaps which seems to be rather popular judging from how often I see them on other blogs or websites. There is a basic free version which really is very basic - there are two map styles to choose from, you may zoom in on the map (but not in detail), and you get stats on country totals. If you upgrade, which costs $1,99 a month, you get to play around with a whole lot more features.
Not all too fond of those red dots I soon progressed to the next widget that caught my attention. Who.samung.us is also a free service which may be upgraded for a fee starting from $5,00 a month. The basic version is pretty neat though with ten different maps that you can personalize with your preferred pins, and the zoom is comparable to the one from ClustrMaps. Unfortunately the free map doesn't offer stats on visitors by country though.
Then I found the coolest visitor widget ever (so far, that is). Revolver Maps gives you not just a map but the planet Earth revolving (hence the name) which is really neat (or maybe I'm just easily impressed by fancy little thingys like that). You have the option to "only" put a 2D map on your blog too, though I obviously chose the revolving map - there are nine different ones to choose from, and you may play around a bit with other settings too. Apart from all that I love how you get global statistics, not just countries and regions but cities too. Not to say those stats are very accurate seeing how I will show up as a visitor too every time I do something on my blog, but oh well. I didn't find any info on upgrades, then again you already get a whole lot for free here anyway.