Risk variants
The modification we play most of the time is to Risk cards themselves. We found suddenly receiving 8 or 10 troops in a country of your choice too powerful (how anybody plays with the progressive-risk-card-reinforcement rule I don't know). So we decided that you only got the two reinforcements in the country on the card. The alteration is that it applies even the country is an oponent (we call it the Paratrooper rule). If you have paratroopers they just attack that country like normal.