Here is what I have seen used in tournament to give you an idea of what can work, its Hybrid @ 2000pts (fairly Balanced) and if your going smaller then a lot has to change as the overall effectiveness of Eldar is totally dependant on how all the units work together and not neccessarily the strength's of the individual units.
HQ 365-18.25%
Eldrad
Avatar
Elite 226-11.3%
6 Fire Dragons, Exarch with Dragons Breath Flamer and Crack shot.
6 Fire Dragons, Exarch with Dragons Breath Flamer and Crack shot.
Troops 669-33.45%
10 Wraithguard, + Spiritseer with Conceal.
5 Pathfinders
10 Guardian Defenders with Brightlance platform, + Warlock with Conceal and a Singing Spear.
Fast Attack 338-17%
1 Vyper with Eldar Missile Launcher
1 Vyper with Eldar Missile Launcher
8 Warp Spiders, Exarch with Duel Death Spinners and Withdraw.
Heavy Support 400-20%
1 Falcon, Pulse, Shuri-cannon, Catipult, Holo-field, Vectored Engines, Spirit Stones, and Star Engines.
1 Falcon, Pulse, Shuri-cannon, Catipult, Holo-field, Vectored Engines, Spirit Stones, and Star Engines.
Totals 1998pts, 11 Scoring Units, with 53 Figures
Obviously Eldrad, Avatar, the WG and Guardians work as the "Fearless Anvil" slowly advancing forward as Eldrad uses his powers to Fortune appropriately, etc. The Spiders and Vypers run the flanks providing mass shooting or templates as required. The Falcons have a number of options with the Fire Dragons, they can deliver both units for mass anti-tanfanty shooting (with flamers) or they can take down tanks very quickly. Devination allows you to re-locate a portion of your forces if needed (before the game) and even Escalation is not that bad to deal with.
Now for local gaming and in many compititions I personnally take Saim-Hann style armies that use Jetbikes and other fast compononets esclusively; but, these types of armies are much more prone to total failure or total success. The options with Eldar are so vast its unbelievable, feel free to check out my website (klucas.piczo.com) where you can read a little bit about all of the units and the different Craftworld styles.... as this may help you decide what type of force you eventually want to have.
Like I said, if your starting smaller, then you really want to consider how the units can work together before just buying a bunch of stuff. Feel free to ask any questions you like and I hope I can help you out in some way.