Since we already have Space Marines on our Minds from Last Weeks article on Vulkan and his lot, I would like to segue into the other most viable build (imo) from the Vanilla Codex. Bikers. This list is far more tactical of a build then Vulkan marines were from last week, but it also is less varied, typically sticking to a pretty narrow range of units. However, this is part of their strength as they are very flexible and can be extremely deadly to an unprepared opponent. Let's delve deeper after the jump...
Biker marines take advantage of the special rule for Company Captains (or Korsarro Kahn) which allow for Space Marine Bike Squads to be taken as troops if the Captain (or Kahn) is on a bike himself. Bike squads, though more expensive then the typical Space Marine Tactical squad, also has some advantages. Though they lack a heavy weapon option (which would be pretty fucking awesome considering they are relentless), they can opt to take 2 special weapons, giving them much needed redundancy. They are also far quicker and more survivable due to the bikes improved movement profile and toughness boost. Finally, their medium/close range shooting is increased due to the relentless rule (which allows them to fire a single shot at 24" even after moving) and twinlinking of the bolters on the bike. Also, they can assault after rapid firing, which is a small bonus (you won't be assaulting much, unless you take a command squad, see below).
However, taking bike squads instead of tacticals in rhinos or razorbacks leaves your army far more vulnerable to anti-infantry weapons and the inability for bikes to change levels in ruins can cause some serious issues depending on mission. Like any other choice in your army selection, it is a pros and cons choice, which should certainly be evaluated before building the army. However, considering the overall ineffectiveness of Space Marine Tactical Squads, I feel this build certainly has its upsides.
Captain with Bike - The piece that unlocks bike squads as troops, and nearly the only time a Captain is taken (typically losing out to a special character or librarian). In this particular list, he really isn't terrible. Give him artificer armour and you are looking at a T5, 2+/4++ model which moves 12 for about 150 points. Most people also give him a relic blade so he hits at Strength 6.
Korsarro Kahn - Some people prefer this White Scars special character to a basic captain. While personally I don't think he is worth the extra price, the advantage of being able to run on his bike can be reasonably useful, and his weapon causing instant death is alright. Overall, however, he is more expensive and not that much more effective. YMMV of course.
Bike Squads - The literal core of the army, these guys will make up your troops choices. Depending on the size of the game, you may want a couple of full squads or minimum sized squads. The advantage of large squads is that they can combat squad for better board coverage, or give you many ablative wounds for the attack bike. The attack bike should always be taken when possible and also given a multi-melta. The mass bolters can handle infantry well enough most of the time, no need for a heavy bolter (if you are expecting lots of foot based lists, taking a flamer squad is superior to taking a heavy bolter anyway). 2x Melta- or Plasma- Guns is typically recommended and some favor giving the sergeant a Power Fist for opportune vehicle assaults. I think its a reasonable idea if you have the points, but remember to maximize you guys, as you will be low model count.
Attack Bikes - In addition to the Attack Bikes within the standard squads, typical bike lists will have 1-2 squads of dedicated Attack Bikes for tank hunting. Others simply favor more standard bike squads, who give you slightly less melta potential, but extra wounds, extra bolters and most importantly scoring.
Command Squad - Command Squads can be given bikes. This creates what is essentially an elite Bike Squad, which can be given upgrade CC weapons, multiple special weapons and has FNP from its apothecary. On one hand, the Command Squad gives a very useful CC punch to an otherwise poor in CC army (not individually that bad, but low in numbers). However, the unit does not score, is only 5 bikes in size, and worst of all costs a fortune for a fairly easy to kill unit. They will easily get mopped up by dedicated CC units in other armies unless given Storm Shields, which can push the price of the unit upwards to 300-400 points. However, some still swear by them so give them a try and see what you think (and give me feedback!)
Like any quick moving army, you should have a speed advantage over most armies. Use this advantage to isolate parts of your opponents force. Remember that your lack of vehicles means far more attention from heavy weapons like lascannons and krak missiles that ignore your armour save and increased toughness, so always do your best to have cover. Overall, be cautious but close ground, since you lack significant long range firepower. You should really start to shine after the first turn assuming enough of your force survives.
Anything you are close enough to shoot at effectively will likely be able to assault you the following turn, so when approaching a unit to fire at them I suggest concentrating the firepower of multiple squads to ensure the squad is dead or weak enough for the bikes to finish in CC. Take advantage of combat tactics to keep your bikes out of CC, since you should fall back well out of pursuit range and automatically regroup. Lastly, don't ever reserve everything against armies with infiltrating Kroot. We all know how that ends...