Not necessarily what you play the most, but the boards you think are the best of the best.  Choose your own criteria.  I'm going to make this a tough exercise for myself because I mostly play my own boards ..but I'm going to exclude them from my list.

In no particular order. I reserve the right to change my list..

Pirates of the Caribbean - Subtley sophisticated

MicroMission - A miniature masterpiece.

Colossal Crusade - Not a fair 2 or 3 player game by any stretch - but what Risk should be AFAIC

Pangea: Rise of the Chimp - Innovative and Fun

Total WarGear - very complicated play - too much for me really, but clearly a fabulous design for play. In the semi-sequitur department, Invention could have very well been on this list, but I find it too convoluted ..or probably just don't understand it enough to warrant its inclusion on my list.

Top Dueling Map: Iwo Jima - I suck at it so I don't play it, but it's clearly a clever and well-implemented design.

My criteria is for the top 5 boards that I enjoy playing the most. This list would probably change for me in a month or two, so it just reflects where I am right now:

-Seven Redux / Seven

-Capital Crusade

-Colossal Crusade

-Pirates of the Caribbean

-King of the Mountains

Coffe Capital

Frontierland Shooting Arcade

Fortress

House of Fog

Rent is Due

(Squirrels of Suburbia) 

I'm going to stick to the Top Five, despite some of y'all...

Gates of Hell - Favorite all around. Fun with teams also.

Battle of Waterloo - Favorite duel board. Tricky.

Capital Crusade - Newest favorite board.

Invention - What risk should be AFAIC.

Happy Holidays - First board I won at this site. Turns out it is more interesting than it would first appear.

Tough Question... In no particular order

Pangea Rise of the Chimp 

StarGear 

Balance

Ren Wars

War of the Roses

Honorable Mentions:

Invention, AvA Tech, House of Fog, Kursk, Iwo Jima

top 5 all time?! sheesh. that's a tough one.

I'm going to take from above and say these exclude any of my own boards, where i might have 2 favorites of  . And these are my first draft. I might have to go back and do some critical thinking to change the list. 

Hex Void: my newest favorite. big enough for large numbers, yet capable for decent games with smaller number. unique enough that it's not the same as a WGWF, but still plays simply.

Rescue: Unique, strategic, simple.

Kropulu Sector: I was super happy when this one got ported over. Still one of my all-time favorite boards.

Chutes and Ladders: I've had more fun on the risk version of this board than i EVER did playing this with my kids (or as a kid). you seeing a pattern of the somewhat simple here? i am...is that good or bad?

Of Kings and Men: Has almost everything except Artillery (outside of factories). simple board; but extremely variable in numbers of ways for play. 

Pangea - Rise of the Chimp: Completely unique when this came out (is it still?). By far Alpha's best work here. Though somewhat disappointed Risky didn't come up with this one!

and now i notice i have 6...oh well. 

Castles -- I think my all-around favorite board, though I don't play it much these days. Great concept, great execution, and very fun and repeatable gameplay.

Axes and Allies -- still one of the best asymmetric strategy boards. Plus, I liked it so much I made my own LotR adaptation =D

Gauntlet -- Another classic, and even though it's broken in terms of balance, I love how the meta-game changed over time to account for green and yellow advantages. Some great games on this board I recall fondly.

Spy v Spy -- one of the simplest and best dueling games out there that still allows for a huge amount of strategy. I love that it boils down to which player is a better judge of exactly when it's time to take the big gamble. Spy vs Spy was one of the inspirations for me to make Dolmabahce Sarayi.

Mall of the Dead -- luck is a huge factor, but somehow this board never disappoints for a quick and gory game.

Infection -- How could I not include the board that introduced the concept of hordes-style bonuses to the world? This is such an integral feature to so many boards now, and all because Cram (aka Reich) made this board (well, the original, anyway, which was simply titled Hordes!).

Currently, but subject to future changes and in no particular order:

Civil War

WarGear Warfare (always)

Iwo Jima

The French Resistance

Battle of Bladensburg

I'm actually surprised at how diverse the choices are. I count, with 8 people weighing in, a total of 38 unique boards that made the list. Pangaea: Rise of the Chimp made three people's lists, and Iwo Jima, Colossal Crusade, and Capital Crusade each made two people's lists. Not much overlap!

Kjeld wrote:

I'm actually surprised at how diverse the choices are. I count, with 8 people weighing in, a total of 38 unique boards that made the list. Pangaea: Rise of the Chimp made three people's lists, and Iwo Jima, Colossal Crusade, and Capital Crusade each made two people's lists. Not much overlap!

I was noticing the same thing. Very interesting.

Never played "Pangea: Rise of the Chimp" so I just joined an open game to try it out. Come join us at:  http://www.wargear.net/games/join/506044

Fallout

Day at the races

Fall of Rome

Game of Hordes!

Tree of death

list subject to change without notice (if im in a bad mood or not) 

renaissance wars

wargear/global warfare

medieval europe

castles

anarchy

Colossal Crusade

Battle of Waterloo (This board feels like a real game of chess every time I play. I'm not very good at it, but it feels like DukeofWellington and I have had games going on it regularly for at least the past year.)

Risk of Thrones

Wargear Warfare - Still love the original.

Capital Crusade - I know it's pretty lame to choose my own board, but I really enjoy playing on it.