The Eldar Vyper is a cool little fast attack unit, it is about the same size as a Dark Eldar Venom and can deliver nearly as much fire power for about the same cost points.
Know your Vyper
Even though the Vyper is mentioned as a jetbike in the fluff, take note that is actually a skimmer vehicle and has the same profile as a Dark Eldar Venom - 10-10-10 HP 2 open topped. Base points cost for the Vyper is a very reasonable 50 points.
Vypers can be taken in squadrons of up to three, so bring some friends!
Standard weaponry is a shuriken cannon and shuriken catapult. You can upgrade the shuriken cannon for: starcannon, bright lance, scattter laser or eldar missile launcher. Out of these upgrades the starcannon is the cheapest at 5 points with the eldar missile launcher being the most expensive costing 15 points; the other two are in the middle. You can also switch the shuriken catapult for a shuriken cannon for a cheapo 10 points.
Out of the upgrades above I would only consider weaponry which has multiple shots. Leave the bright lance to Wave Serpents which are twin-linked and the eldar missile launcher is too expensive.
Starcannon is ok I guess and can work in squadrons for effective 2+ armour save killing.
I would consider making the Vyper into a S6 skimmer of death; take a scatter laser and a shuriken cannon and you're talking 7 x S6 shots at minimum 24". Keep in mind that the Vyper is a fast skimmer and can move 12" and fire both weapons which extends the range of the shuri cannon to 36". When combo'd with the scatter laser the shuri cannon can re-roll to hit if the scatter laser hits, which giving it has 4 shots the chances are slim to miss every single shot.
If you are stuck for points and need a much cheaper option then take dual shuri cannons. You still have a reasonable amount of 6 x S6 shots at a threat range of 36". Bargain for 60 points!
Pimp yo ride
The Vyper has access to the Eldar vehicle wargear section, which out of these there's only two items I would consider; ghostwalk matrix and holofields. Both these items work nicely as the ghostwalk matrix gives move through cover which means you can land your Vyper inside a ruin without taking dangerous terrain tests. The holofield gives +1 cover saves, so if you're in a ruin that's a 3+ cover save :)
I'll mention that taking just these two items will push the Vyper up to 75 points and that is before you throw on addition weaponry, though for 85 points you could get the dual shuri setup and skim from ruin to ruin without any worries and getting a funky 3+ cover save.
If you think the Space Marine Land Speeder with dual multi meltas costs 80 points, the Vyper for 5 points more is a very good deal considering that it can bring more dakka and is more survivable with upgrades.
As mentioned above, Vypers can run in squadrons of up to three. Having squadrons brings all the usual benefits such as 4" coherency, hits and damage rolls are rolled one at a time and once the model in that squadron has been destroyed then you move onto the next model. If a Vyper in the squadron does become immobilised then it can be abandoned; in kill points this will give up another point while in the scouring it would also give up more points, but produce another scoring unit, providing the model is within 3" of an objective once immobilised.
Like wounded multi wound models, if a vehicle in squadron does lose hull points, then you can jump it to the back of the squadron and have full hull point vehicles at the front and taking the hits.
Personally I run my Vypers in separate units, though running Vypers in paired squadrons wouldn't be too bad. Reason I run my Vypers separately is because they work as a pair and one will zoom up and tackle side or rear armour of a vehicle and then the other can finish the job or fire at the unit inside if the vehicle is a transport vehicle and if the vehicle has been wrecked/explodes. You may also find that the combined number of shots maybe over kill, many times a single Vyper has done the job for me and this allows the second Vyper to fire into a totally different enemy target.
Jumping back to the setups, dual shuri and scatter-shuri are the best setups. Starcannons would work in squadrons nicely and could pump out six shots between three Vypers and make effective Terminator and monstrous creature hunters, but do not expect them to do wonders as against a typical T6 monstrous creature they would only score two wounds on average.
Both the dual shuri and scatter-shuri have the same roles; vehicle hunting and cheap troop killing. Primary targets for Vypers are none transport vehicles. Vypers are fast enough to get in the rear and side armour and unleashing 6 x S6 shots is no laughing matter. Things like Predators, Vindicators, Leman Russes, Chimeras, Ravagers are all nice targets for the Vyper. The reason for targets like these is there's no enemy units inside these vehicles which can then jump out and score some revenge.
Ideal troop targets would be small Space Marine units, Grots, Scouts, Cultists, Long Fangs, Devastators etc. Basically small units or weak units are ideal for the Vyper to cause significant damage on. With range and speed on their side the Vypers can easily reach those units at the back of the board camping in a static position or on an objective. A squadron of dual Vypers or Vypers supporting each other could easily tackle any of the example units with ease.
Support your Vyper
Like every other unit the Vyper needs support and this is more important for Eldar than any other race as Eldar have niche roles on the battlefield.
Wave Serpents support Vypers brilliantly as they can add better bright lance setups to crack open transport vehicles along with the funky shield blasting. This will allow the Vypers to torrent the surviving enemy unit from inside the vehicle with S6 death. Additionally it is possible for the larger Wave Serpent to block LOS to the much smaller Vyper, of course this is taking into account that the enemy unit is at the same ground height as the Serpent.
War Walkers are another unit which is great for supporting Vypers. The lances work the same as the Wave Serpents, but take scatter lasers and you've got some long ranged fire power which will force the opponent to decide on target priority - the supreme dakka dishing War Walkers or the nimble and annoying Vypers racing up the flank.
Warp Spiders match with Vypers nicely. The Vypers can give that bit of armoured threat in an majority infantry army and when used with Spiders both units can advance together and offer the same roles as a nice redundancy package. The Spiders have the shorter range, so the Vypers can dish out some fire power to cover them as they advance, though Spiders will be better at anti vehicle duty as they gain +1 strength for their guns when firing at initiative 3 models or below.
Lets not forget the Saim-Hann Windrider list, after all Vypers in the fluff are highly associated with Saim-Hann. The Vypers will give some armoured threat to an all jetbike army and much more long range fire power as only so many Windrider bikes can take shuri cannons.
Vypers are a cool bit of kit for Eldar and can work nicely in any Eldar army. Do you use Vypers in your Eldar army?