I always figured I was perfectly capable of brushing my own teeth without the help of an electric toothbrush. Then, I got one, and I realized the benefit is actually how gentle they are on your gums. Most people actually brush their teeth way too hard, prompting stern warnings from the dentist about dangerous gum recession. But trust me: Get an electric toothbrush, and all that talk will cease.
Though you can find some drugstore models for around $30, I'd recommend paying a little bit more for a really great toothbrush; they last forever, and there is a very notable difference between the cheap and pricey models. The Cadillac of electric brushes is the Sonicare Elite e7300 Toothbrush. The brush head vibrates at ultra-high speeds and comes with a 2-minute timer to ensure optimum brushing time. Buy it for $94.99 here.
To see a cheaper model,
The round head of the Oral-B 7850DLX ProfessionalCare Deluxe Power Toothbrush rotates and pulses at the same time to get your teeth extra clean. There's even a timer that goes off every 30 seconds to make sure you're covering your whole mouth. It's available here for $79.99.