The Loma Linda Trading Post (a weekly newsletter) is a good place to look for rental possibilities. I am currently a first year ER resident, and I agree with you that Loma Linda, Redlands or Grand Terrace are good target areas to live. If you're interested in a resident spouse's perspective on best places to live near Loma Linda... feel free to visit my husband's webpage at residents.zonacondo.com.
I lived in the area for 6 years (and worked at LLU). I rented a place at "Parkview Terrace" in Redlands. It was really nice, one of the nicer complexes in the area. It was off Barton Road just on the Redlands side, and LLU is about a 10 minute shot straight down Barton. Downtown Redlands was a 10 minute shot straight down Barton in the other direction, so it was pretty convenient for me.
I think Redlands is by far the nicest community in the area, it's got the most stuff to do and has a lot of good places to live. Most of the faculty and other staff I worked with at Loma Linda lived in Redlands, if that means anything.
If you're still looking (or know of anyone who is), I have a condo in Redlands (2 story end-unit) that has 3 bedrooms, 2.5 baths, detached 2 car garage, small private backyard and patio, approx 1400 square feet. It will be available sometime in November and is in a great location. Only a few miles from the LLUMC and walkable to downtown Redlands and all the great shops & restaurants there. Rent is $1500/month.