I don't know enough about the fraternities, but I'll cover the sororities:
Alpha Chi Omega: I love their symphony.
Alpha Delta Pi: I think it's awesome that they were the first collegiate secret society for women and paved the way for the rest of us.
Alpha Epsilon Phi: I love their flower and mascot.
Alpha Gamma Delta: I love their spirit! It seems like every AGD is really cool and full of energy. And of course there are tons of them here on GC.
Alpha Omicron Pi: I love the panda mascot, and how they're original by having only one color and using their flower in place of a crest.
Alpha Phi: I love their flowers, and their crest. I also think their commitment to alumnae initiation is really cool, and I hope other groups follow their lead.
Alpha Sigma Alpha: I love their colors!
Alpha Sigma Tau: I love their flower, and the anchor symbol.
Alpha Xi Delta: I really like all AZD's symbols . . . I think they fit together really well.
Chi Omega: Every Chi O I've met has been awesome. And there are so many of them!

Delta Gamma: I think their website is awesome and so thorough -- it really sets the standard for the rest of the groups. I love their badge. And I think the fraternity-assisted COB thing that they do is wonderful; it really shows the commitment that their HQ has to the chapters.
Delta Phi Epsilon: I think their philanthropy -- for eating disorders research -- is wonderful. I also love their colors and symbols.
Delta Zeta: I love the colors, and the lamp symbol.
Gamma Phi Beta: I love the symbol of the crescent moon . . . since the crescent is a favorite of us Tri Delts too.

Kappa Alpha Theta: I like that their flower is, like ours, a pansy. And I've never met a Theta who wasn't the epitome of classy.
Kappa Delta: I LOVE their open motto. I also think their philanthropy work with the Girl Scouts is really cool.
Kappa Kappa Gamma: I love the key symbol, and their colors. I also think it's cool how they let each chapter pick their own philanthropy to work with. Their badge is really pretty.
Phi Mu: I love their colors . . . I'm a girly girl.
Phi Sigma Sigma: I love that they were founded to be as diverse as possible, and as far as I can see they continue to be one of the most diverse NPC sororities out there.
Pi Beta Phi: I love the angel as their mascot, and their philanthropy of working for literacy.
Sigma Delta Tau: I think the torch symbol is so cool.
Sigma Kappa: All their symbols and colors are so pretty.
Sigma Sigma Sigma: I think their open motto is really cool, and it's awesome how they have a chapter in Germany.
Theta Phi Alpha: I love their colors (same as Tri Delta's!) and the penguin mascot is really cute.
Zeta Tau Alpha: Their commitment to their philanthropy is amazing.
Alpha Kappa Alpha: I love the colors, and the ivy leaf symbol.
Delta Sigma Theta: I love the colors.
Sigma Gamma Rho: I think the badge is beautiful.
Zeta Phi Beta: I love the symbols.
Plus, I love how all the NPHC sorority members are in it for life, and how busy their GC forums are -- I can only wish the Tri Delt forum was that busy.