Rahm Emanuel and I share something in common: we both used to live in Illinois' 5th Congressional District on Chicago's Near North Side. I've moved on to IL-4, where Luis Gutierrez is my Representative, while Rahm has moved on to the White House.
But it looks like a clear favorite has emerged to take Rahm's seat in the Congress, and that favorite is State Rep Sara Feigenholtz. Feigenholtz has two distinct advantages in a wide-open primary field: firstly, she's raised the most money, and secondly, she has the endorsement of the SEIU -- a modest surprise as the scuttlebutt I'd heard was that the unions would be reluctant to endorse in this race given the number of "acceptable" progressive candidates. Although portions of IL-5, such as the Lakeview/Wrigleyville neighborhood, are rather well off, the district extends westward and encompasses a number of poorer Hispanic and "white-ethnic" working class communities; the SEIU's endorsement is a pretty big one in a district like this. FiveThirtyEight, in its excursions around Chicago, has also noticed a small proliferation if Feigenholtz signage/bling in the district.
The most interesting alternative to keep an eye on remains Tom Geoghegan, a labor lawyer and author who has been endorsed by the Cook County nurse's union and has many connections within the netroots. This is one race, indeed, where an endorsement of Geoghegan by some of the major left-of-center blogs could make a fair amount of difference. But if Feigenholtz (certainly no conservative herself) is consolidating establishment support, his road is largely uphill.