I loved Crobat. Its a good annoyer with a fairly decent attack pool. I had one on Platinum that was an absolute beast. It took out Gyms all by itself.

Im currently using an Aerodactyl too since theyre pretty powerfull however if its an actual 'Bird' pokemon you want rather than a flying type then im guessing ur pretty limited.

If its just 'i want a flying type' remember there are things like Salamence, Gyarados, Gliscor and Charizard that fall under flying types.