Nice Thread Idea BTW. Here is my top 10:
10 Raindance - At the time, raindance was a very good deck, and has evolved over the years to Pokemon Center, Energy Flow, etc. It is still very fun and hopefully we will see the resurgance with Blastoise ex.
9 Scizor/Muk/Furret - This won many major events and several players did very well with it espically Ness. It had a chance vs Cargo if you had starmie or mantine. Fun deck.
8 Blaziken - Even with Pokemon Reversal in the format now as a flip for a gust, Blaziken is still the best deck, hands down and will continue to dominate and sweep most of the GC's and maybe even the SCs and Nationals. Its brokenness is intramountable and the ability to Abuse the One Energy Per Turn Rule and Rare Candying like mad is amazing. The speed and power of this deck is tough to match and there is no doubt it will go down as one of the top 10 decks of all time.
7 Typhlosion - This survived quit a looong time, and i believe it was first really popularized by Ness at the ECSTS 2001. With combos such as Blaine's Arcy, Eggy, and even solo it certainly deserves a spot in the top 10.
6 Entei/Cargo - Man this deck was seriously really good. Easily one of the quickest decks of all time, dishing out tons of damage by turn 2 and constant double gusting and OHKOs were common, although Pichu did give it some problems. One of my all time favs.
5 Crobat - Before Crobat was released Rocket On was completely dominated by Gatr, Crobat at least somewhat gave it for a run. A good player with some decent flips could beat gatr with crobat and it was certainly a fun deck. Crobat also gets bonus points for having good card art ;p
4 Wigglytuff - This deck has won so many games all time it is simply unbelivable. The ability to DTW for 60 turn two and 70 with a PP back in hay days was great. It combined with the Haymaker Archtype to create a powerful deck which dominated such events as the first ever STS in Long Beach.
3 Feraligatr - I have always hated Gatr with a passion, but there is no doubt it is a great deck. It dominated Rocket on from Start to Finish, without a doubt. When you dominate a format, you deserve a place in the top 3.
2 Haymaker In All Its Forms - There are soooo many versions of hay including: R.Zap Trap, Sneasel, Buzz/Chan/Scy, its just amazing. The amount of time this lasted and the dominance it had for so long was amazing. Truly one of the greatest.
1 Slowking - Paired with such things as Sneasel, Steelix and the Great Chansey, Slowking has always been a dominant card, the ability to shut down trainers and trap your opponent is broken. Combined with Sneasel or a great wall in chansey the deck becomes impossible. Truly the greatest.