If you are wanting to use the Kill Team formations (possibly in conjunction with the Black Spear Strike Force Detachment), the general consensus on the 'net so far is that the Aquila Kill Team is the best for a "take all comers" type list, as the re-rolls it grants are useful in all situations, not just against certain battlefield roles.
As Killersquid mentioned, the Frag Cannon looks pretty good, and a lot of folks are planning on making a drop-pod team with 4 of them in the squad for a nasty alpha-strike unit capable of taking out anything that might scare you.
Most things that work for Sternguard in standard Space Marine lists should work here too. Drop-pods filled with Combi-Meltas, Combi-Plasmas or Combi-Flamers allow you to hit a specific target when you drop in, but keep versatility via the bolter's Special Issue Ammunition.
Don't miss the added rules you get in a Kill Team that has Vanguard, Bikers and/or Terminators added. Heroic Intervention (Vanguard) on a close-combat oriented team is helpful. Split Fire (Bikers) can help spread the love with your big guns in a shooty unit, and Fearless (Terminators) can help a team hold the line when needed.
Also, don't forget that your Librarians have access to lots of different Psychic disciplines, so you can tailor the types of powers you shoot for based on how you want to run your teams.