I agree with Vulcan. The Dark Elves don't have any useless units in their book, they just need different strategies.
For fun units, there's Corsairs as a solid core choice. These guys pump out a lot of attacks if given extra hand weapons and with the right magic support they can cut almost anything to pieces. In a game I played today I had a unit of corsairs who wiped out two units of 12 Chaos Warriors and was still charging around the board completely fearlessly despite the fact that there were only four left (out of a starting number of 28)
For long range firepower Dark Elves have Repeater Crossbows. These things can rip lightly armoured units to pieces. Each basic crossbowman can fire 2 shots a turn so you can get a lot of shooting from a small unit. They're the same statline as the basic Elf spear wielding warrior so these guys can also hold their own pretty well if they end up in combat. For more accurate and sneaky shooting there's also Shades. These guys are great for harassing light units and taking out war machine crews, so it's usually worth finding a way of fitting some of these guys in.
As other units go you have the (rightly) feared Black Guard. These guys pump out a lot of attacks and will very rarely run away, meaning once they're in combat the opponent is going to have to kill them to the last man. I often use these guys to hold an enemy in place whilst I get a flank or rear charge in place. Only downside is they're quite squishy and can only be taken in limited numbers (maximum unit size is 20) so against high strength enemies they will die quite quickly but that can be said of most Dark Elf units.
Executioners are one of my favourite units, despite them being fragile and often seen as being not as useful as other units in the book, unless taken in large numbers. Killing Blow gives the chance of instantly killing an enemy with no armour save allowed. This combined with the high strength attacks from their great weapons make these guys perfect for cutting through heavily armoured units such as Knights or Chaos Warriors. Ideally you want these guys to hit a flank to minimize the number of attacks coming at them as they strike last. They can also be a pretty good unit for holding an enemy up if you keep a Cauldron of Blood near them as it makes them less likely to flee from combat.
Magic is a thing which Dark Elves can really excel at, if you like to take occasional risks. They have access to lores of magic which offer a range of buffs and hexes and pure damage. Combine this with their special rule which means they can use as many dice as you want to cast spells (other armies are limited to using six) and a bonus spell which allows you to make more dice for casting and it means you can dominate the game in the magic phase, with a bit of luck and the occasional mad decision to throw all of your dice at one spell

Be fearless and aim to completely dominate you enemy, it helps a lot.
We Dark Elves also have lots of nice beasties to play with. The War Hydra is a lovely unit which can wreak some awesome havoc. Add to that Dragons, Pegasi, Manticores and Cold Ones (basically Velociraptors) as mounts for our Heroes and Lords (and elite cavalry in the case of Cold Ones) and you have lots of nice choice to suit your play style.
Then there's the Dark Elves special rule, Eternal Hatred. This means that your Dark Elves will hate everybody, granting re-rolls to hit in the first round of close combat (or every round if you're fighting High Elves, we hate them A LOT). As you're going to need to inflict maximum pain in that first round as Dark Elves can't take a lot of pain back these re-rolls are invaluable.
Pretty much look through your book and pick the units which appeal to you. There's no wrong choices here so as long as you build your tactics to suit your playing style you shouldn't go wrong.
As a starting point, I'd recommend the Battalion box. That gets you a good solid amount of core troops and some Cold One Knights.