Aye, get a database from Maxmind. The free one is decent, but the paid versions are obviously better.
I wouldn't just block them. Redirect them somewhere, (dialer, or AFF or something.) where you might at least have a chance at getting something out of them.
Simply add:
GeoIPEnable On
GeoIPDBFile /path/to/GeoIP.dat
RewriteEngine on
RewriteCond %{ENV:GEOIP_COUNTRY_CODE} ^XX$
RewriteRule ^(.*)$
http://www.shitcountry.url [L]
XX would be replaced by the code for the country in question. If redirecting numerous countries to the same URL don't forget to add [OR] after each RewriteCond statement EXCEPT for the last one. If redirecting numerous countries, each to different locations, you'll need one RewriteCond statement AND RewriteRule for each.