Welcome gmaninboston! I live in Southborough, and have two kids under seven. My DH and I had similar issues, with similar imbalanced salaries. We've had various different child care arrangements over the last six years, and all have their pros and cons. No child-care arrangement is perfect, so you just have to find what works best for you.
We started with daycare at my work--45 min commute with an infant through boston traffic. Great that I could see her during the day, but commute + inflexible hours, closure on every school holiday made it a bad choice in the end.
Nanny--first summer, while I worked 4 days per week but school daycare was closed. Nanny was challenging to find initially, and expensive at $16/hr plus taxes, but she was great. Biggest drawback was lack of socialization, but we never dealt with issues of sick days, etc that many of my friends have experienced with a nanny since it was just for the summer.
When I went to part-time we moved to a daycare in our town. It is wonderful. It is a local center with two locations, called WeeCare for Little People. May not work depending on where you live, but we have been very happy. It isn't cheap, but less than the major centers like Bright Horizons. I've been back to full time for two years now, and we pay a lot for child-care but I think my kids are getting a better experience there than they would be if I stayed home full time.
Feel free to PM me if you'd like. Best of luck finding something that works for you!