Departamento Americana on the JF Kennedy express in Santo Domingo has a good appliance section - just don't buy any floor models or "the last one we have"s.
Carrefor's on the Duarte highway going north on the way out of Santo Domingo to Santiago has a good selection of appliances, just lousy sales help. Good delivery service though - a bunch of independents out in front waiting to haul it away for you at a reasonable price.
And, I've used the service guys from Plaza Lama, and they came out about 2 days later, fixed the problem on the washer, reasonable cost, and it was fixed right (knock on wood). Plaza Lama though, has GOT to have the worst bunch of sales creeps (I mean salespeople) in this hemisphere. It just makes you grind your teeth.