There were many different generations of the Bonneville. The first generation Bonnevilles were sold from 1959 to 1970. Some distinctions on those cars were the split grille and wide track, both of which would become trademarks of the Pontiac brand. The Bonneville was the top model in the Pontiac lineup.
The second generation Bonneville was sold from 1971 to 1975. This was the first time the Bonneville would not be the top Pontiac model, as it was usurped by the Grand Ville. The only three body styles were the 4 door sedan, 4 door hardtop, and 2 door coupe.
The Bonneville was reduced in size for the third generation in 1977. They were once again the top flagship model made by Pontiac. This generation would end in 1981.
The 1982 to 1986 Bonnevilles were more boxy and lighter than the earlier models. A V6 engine from Buick was now standard equipment, although the V8 engines were still an option. These G bodies were previously named the Pontiac LeMans. These would be the final years of the rear wheel drive Bonnevilles.
The 1987 to 1991 Bonnevilles showed some strong improvements over the previous generation. In fact, the 1987 model made Car & Driver's Ten Best list.
The final generation Bonneville, sold from 1992 to 1999, was a major redesign for the car. There were also some special editions of these cars, including a supercharged version. The Eaton superchargers on these Bonnevilles helped boost output to levels not seen in decades.
There are plenty of Bonnevilles out there on the used car market. There are some great deals on eBay. Make sure there is little rust and not too many miles.