You don't mention a preference in engine size or cost. IMHO a reasonable entry level, .40 size, funflying bipe is the Thunder Tiger 'Tiger Bipe.' I used mine to develop awareness of the slightly different flying charactersitics of a biplane. Enjoyed flying it.

But, not as much enjoyment as I get putting my Midwest 'Super Stearman' through it's scale-like aerobatic routine!