With that many cards you can definitely make quite a few decent decks. You may even be able to make 2-3 semi-competitive decks. To make a really competitive deck you'll need to do some buying/trading. If you want to be competitive, I recommend scouring these forums to find out what's good and what playstyle you prefer and then focus on making a tier 1 version of that deck. Here's a brief list of some of the tier 1 or 1.5 stuff:
Black Ice - Alliance Mage hero from Hunt for Illidan. Uses interupts to control tempo and Water Elemental and Myriam Starcaller to win the game. Fairly ally focused. Long considered the best deck in constructed. I think it's starting to be overshadowed though.
Kil'zin of the Bloodscalp - Horde Traitor Shaman from Servants of the Betrayer. This is a rush deck. Plays low costed daggers such as Whispering Blade of Slaying and Retainer's Blade for quick damage and a good effect (on Retainer's Blade). Also runs a fair amount of burn and several cheap allies that pack a punch (Bloodsoul, Offender Gora, Sha'kar). It has a good number of answers to other decks for a rush deck.
Witch Doctor Koo'zar (may not be tier 1) - Troll Priest from Drums of War. Balls to the wall rush. Tries to swarm the field as fast as possible. Can win very early but most decks have good answers to it if it can't pull the win out fast enough. Shadowfiend is the stand out card in the deck.
Varanis - Promo Blood Elf Mage. Focuses on playing Slow, whcih only allows your opponent to play one card per turn, and then controls game with interupts. Gets the kill with Belt of Blasting.
Vorna the Wretched - Traitor Blood Elf Mage from Servants of the Betrayer. Plays a lot of tempo and control cards to stall the game until she can play Illidan Stormrage master hero. Several other decks are made using this win condition (Illidan) as well.
Mythen of the Fang - Alliance Traitor Druid from Servants of the Betrayer. Plays lots of small untargetable allies to rush the field. Also plays a fair amount of ally control (Moonfire, Wastewalker Helm combo) and Form of the Serpent.
Lionar the Bloodcursed - Horde Traitor Warrior from Servants of the Betrayer. Another rush deck. Runs all Orc allies to take advantage of Orgrimmar. Stand outs are Kazamon Steelskin and Reghar Earthfury. Allies are larger than other rush builds, but the deck is somewhat slower than Kil'zin or Koo'zar.
There are undoubtedly several more, but this is what I could come up with off the top of my head. If any of those sound interesting, let me know and I can hook you up with more details on what they use. Good luck! ^__^
PS - Scourgewar sneak peek is a great way to start. Everyone gets roughly 6 packs and has to make a deck. More casual atmosphere and you'll be playing on an even field.
Click for trades!!! ^___^
http://entertainment.upperdeck.com/WOW/COMMUNITY/forums/thread/1896175.aspx