Pistols and Chainswords with Jump-packs. There's really not much else to say about these guys.
Taking up a Fast Attack slot, they're a handy little group useful for getting around or behind enemy troops and tying up their important units with a little melee.
Highly useful against Tau due to their low Weapon Skill and Strength, these guys will eat them up. Other than them, I plan on shooting them towards Heavy Support units. Devastator Squads, Heavy Weapons Teams, even tanks. I've equipped them with Melta Bombs just to ensure that they have the capability of filling that role.
Melta bombs are hot (pun!) when given to Assault Marines. Due to their high movement rate, I can take those bombs to the target vehicle's rear/sides where the AC is generally weakest.
As for my other two Fast Attack slots ... what kind of Dark Angels player would I be if I didn't field some Ravenwing? One Ravenwing Assault Squad and one Ravenwing Support Squad.
That's 6 bikes, one attack bike, and 4 landspeeders total!