Low-budget: Super 8 right outside Watertown Square. Best Western Terrace Motel, or the Days Inn, in Brighton. They are what they are.
Higher-end: Doubletree Suites in Allston (just off the Mass. Pike exit), the Newton Marriott, or the Westin in Waltham.
For much more in-depth info consult Yelp or TripAdvisor.