When I first started playing 40k "back in the day" I started with Ultramarines (like everyone else), and the artist in me decided to throw in a squad of Imperial Fists for the color change on the table-top... more than anything.
After I sold my Ultramarines, I decide to play Space Wolves to join my bio-bro on the field of battle, but since he was already playing Ragnar's Company, I decided to field the Great Wolf himself--Logan Grimnar! (This pic is a spectacular painting of Leman Russ, Primarch of the Space wolves)
I loved playing Space Wolves, and the versatility that they offer... but at the time I was playing, it seemed EVERYONE else figured out what my brother and I knew, so I sold that army off and decided to field an entire army of Imperial Fists!
They looked tremendous on the Battlefield (yellow against most table top gaming colors really stands out!), and then I came across rules for the Deathwatch Space Marine Kill Teams! With access to M.40 Targeters to affix to the Bolters and Stalker Silencing shells which force pinning tests, not to mention the ability to bring in TWO Heavy Bolters with special ammo and suspensor links which allows you to move and fire, it wasn't hard to start salivating...
(click any pic to enlarge)
In truth, however, the thing that I love MOST about Kill Teams, is that the members a chosen from the very best the Space Marines have to offer, which means each member is hand selected from any chapter! The only assemblance of their past loyalties is the right shoulder pad which bears their original chapter badge; so you can incorporate members from different chapters, and combine them into one unit! How cool is that? Each Marine wears the Black Armor of the Deathwatch, with the Inquisitorial seal and Crux Terminatus on the left shoulder coupled with the steely, heraldic armored gauntlet reminiscent of the knights of old!
Here is a brief trailer from "Ultramarines: A Warhammer 40k Movie" with a squad of Ultras, led by an Imperial Fist Chaplain, and Fist Veteran Sgt! Enjoy! ;D