We like interns a lot - bright students can actually do a lot more than people expect, they help create a culture of enthusiasm, and they represent our best pipeline for new-grad hiring. We go to local college job fairs in the Fall and collect resumes. This consistently works - we get 100s of resumes from juniors and sophomores, winnow it down to phone screen around 10-20. We in-person interview 3-7 and hire at least one, often several.
It takes a little more effort than just posting to job boards (and is more expensive - the colleges charge money for the fairs, plus you have to have someone stand there at the table and accept resumes). However, it's extremely reliable: this portion of our company has been on autopilot for a long time now. If you have the cash to spend, I think it's good value relative to general recruiting expenses. You can't build your whole company this way obviously, but I think there's a place for it. It's at least easy.
Regarding non-Summer interns, we have encountered students at the job fairs looking for something like that. However, it's low numbers, so the odds you find one that's a good fit aren't very reliable.
The one program in the Boston area that works for us during the school year is Northeastern - they are built around the idea of a co-op program. Every student does 2-3 full-time, 1 semester internships (it's a 5 year school; 4 years of class, 2+ semesters of internships). I don't know of another school like this; it's worth considering. Students prefer to stay local (they keep their housing), but they might be intrigued to travel to where you are if you could help figure out housing for them. This definitely represents more expense (your flight out, plus paying them enough to fly to you and deal with temporary housing for 4-6 months), but it is reliable - depends on how important this is for you to get done. Relative to the cost of a full-time hire, it's still pretty inexpensive.
The other surprisingly quality source of interns has been to go to the people on our extended team who are in their 40s and 50s (i.e. executives, advisors and investors) and ask them to tell their friends who have college-age children we're looking for someone. It's low numbers, but it's been nearly 100% hire rate when we do get recommendations that way. It's kind of a weird way to use your extended network (that is usually otherwise devoted to finance issues, at least for us), but they don't seem to mind at all - and it's usually been a very positive experience for everyone involved; keeps a "family feel" to the company and reinforces relationships.