This subject has been one of the most popular subjects here on the PFRE blog for many years. Here is what I used to recommend. But over the last year or so things have changed. I feel the need to rewrite my recommendations. Here are the ground rules:
OK, given those basic ground rules here are my specific recommendations for good quality gear at a reasonable price:
#1 above is the best choice but #2 is workable if you are really tight on funds. There are other assorted items you'll too but these are the basics.
I used to recommend cropped sensor Canon and Nikon DSLRs for getting started in real estate photography but after using the above equipment I believe it is at least technically equivalent to Canon and Nikon cropped sensor gear and clearly superior in the aspect of size and weight.
Update 7/15/2016: My point in this post is not so much that real estate photographers can replace their Nikon and Canon gear with a mirrorless camera but it is now a LEAST COST alternative. You can get a new body/lens for $548 (#1) to $947 (#2).