In 2008 I bought Risk 2210.  Then through board game geek I discovered many variations.  After trying a few of those methods listed there, we started creating our own variants.  We played once a month and every month there was a new twist or added element.  Some worked, some failed spectacularly.  As a club we played our 70th game at the end of 2015.  Add in games I played with family and other friends and I've played risk close to 100 times.  This site details the many methods we've tried, styles and strategies and other risk related thoughts.

Risk 2210 A.D. House Rules
I greatly prefer Risk 2210 to classic Risk.  The water colonies and lunar territories significantly increase your diversity of options.  The Australian continent is no longer isolated from the rest of the board.  However we've made some customization to the base rules that I highly recommend.

I guess more officially they're non-player controlled antagonists, but they fulfill the same role.  Computer players can be a lot of fun and they can be very frustrating.  They all slow game play because each round or sometimes each turn you have to do a side bit to resolve their actions, but they do add to the fantasy element of the game and quite often I generally get more psyched for games involving a computer player.  It's been my experience that it is a lot more frustrating for the individual if they are killed by a computer player instead of by another human player, but it's more fun for the rest of the table to watch the computer player kill someone off.  Sometimes they fulfill a unifying role forcing more alliances as players have to team up against a particularly powerful opponent.

A new map is a great way to add variety without complexity.  I feel the key to a good map is it should bring some new dynamic to the table.

A key part of risk is the informal alliances players make to bring down others and those alliances eventually crumble for there can be only one winner.  These methods look at more formal ways to bind players together.

Small changes to the operation of the game that keep players on their toes as they have to adjust tactics to deal with new situations.  Most combine easily with other methods.

These are custom scenarios designed by my group.  Taking inspiration from film, literature and history.

Most of my Risk games involve Risk 2210, but we have branched out into several other variants.

Other War Games
Sometime after game 50, risk night evolved into war game night.  Mostly risk still, but we've diversified slightly.

I highly recommend Imperial.  It's a World War I game where you play a rich Swiss investor and through donations you direct countries to do your biding.  There's even more shifting alliances and deals than you find in risk.  My favorite part of the game is working out said alliance and deciding which countries will be on top.  It's a little less personal to because if the country you're backing is getting teamed up against then you just start backing a different country so everyone is in it to the end even if some countries fall way behind.

The Game of Thrones Board Game is also a lot of fun if you're a fan of the series.  There's a lot of dynamics of the show built into the game, but that of course means a complicated rule set.  Although a longer game, it is shorter than risk, especially once everyone in the group is used to the rules.

For a long time people have been telling me that if I like Risk then I should play Axis and Allies.  There are a lot more aspects it takes into consideration when designing its battle mechanism which gives a realistic feel, but it's just so long and complicated and I say this as the person who regularly plays 5-7 hour risk games.  So far I've played twice and I'm undefeated (once as Axis and once as an Ally) and I'm sure I can get talked into another game but I won't be the driving force behind setting up that game.  If you do play, don't play with 5.  The player who gets Russia is just royally screwed over.