Finding an apartment in Boston is all about timing. Unfortunately, your timing is a bit off Boston has a fairly predictable renting season. Renters know that students need housing in Late Aug/early Sept. They start asking their current tenants around March/April if they will be renewing their leases, at least in the Allston/Brighton area. You'll see a lot of postings come up for Sept leasing as spring approaches. This has always been my experience and the realtors have told me as much.
In my personal experience, I've had luck finding places in May... June can be a bit trickier. I wouldn't worry too much if May/June is the only time that you can look. I've had good experience using realtors; they're the ones posting all those rooms on craigslist anyway. AND you can screen for no fee apartments and apartments where the landlord pays the realtor fee.
Never take a place sight unseen! Apartments have their quirks around here.
I also really like Cleveland Circle EXCEPT Strathmore RD. Don't take an apartment that faces the street because it is noisily littered with drunk undergrads and some frat houses. This is a main cut through road to the B line for boisterous Boston drunks to clamor down after bars are out.