My favorite steakhouse would be Gallaghers Steakhouse on S. 6th Street. Great service and better steaks that I can make at home. I'm not particularly a rib eye fan but their black & blue ribeye is awesome. Great toonies too.
2242 S 6th St, Springfield
More info: (217) 522-8888
I am also a fan of Saputo's Italian downtown. They are open a bit later...11P I believe. I like their veal parm and the pizza looks damn good.
801 E Monroe St.
I am in Springfield at least once a year on business and am always in the downtown area, so all my suggestions are in walking distance of the Hilton, Abraham Lincoln Hotel, and convention center nexus. One restaurant I just tried in July and highly recommend is:
Caitie Girl's: http://www.caitiegirls.com/ Decor is fun and whimsical, all the staff was very friendly, food was unique and tasty and not overpriced. Local business owners recommended it as "a twist on comfort food." My colleague had the mac n cheese which had pulled pork and pepperjack cheese in it -- delicious! I had falafel tha came with a delicious side salad that was topped with blueberries, strawberries, corn (sounds wierd, but yummy!) and a nice vinaigrette. It also came with beet chips.
Trout Lily Cafe was also good. Had lunch there. It's small, nothing fancy, but I had a good piece of quiche and a curry couscous salad and delicious blackberry jasmine tea!
The Feed Store was also good for lunch. Variety of sandwiches and side items.
Linsday's, which is the restaurant in the A. Lincoln Hotel, is decent. Although I try to stay away from hotel restaurants, their prices are good and staff is friendly. I had a pecan-crusted tilapia that was really tasty. Their corn chowder is also delicious.
Sammy's Sports Bar & Grill is good if you're looking for casual, inexpensive bar food. You must have the Horseshoe, a Springfield specialy. You have your choice of sandwich, which is topped with french fries, and then a cheese sauce! Completely unhealthy but worth trying. Make sure you have a couple brewskis to wash it down! Cheap beer! It was a perfect end of a long day at a conference for my colleague and me. It's also good if you want to catch a game ... lots of tvs.
I must also say you should go to Del's Popcorn Shop -- not for a meal unless you love popcorn! They have great homemade popcorn (cheese, caramel, candy, kettle) and candies. Great for a late-night snack back at the hotel.
I've heard good things about Augie's Front Burner ... a long-time locally owned establishment that's a bit more upscale. I just did not make it there on my last trip.
A few ideas:
Coz's, IMO the best Pizza in town. Really 'downscale'...friendly, local bar feel.
D'Arcy's: a much more extensive menu. Pub food that is better than it needs to be. It has probably the best example of a Springfield specialty, the Horseshoe sandwich. Pours a proper Guinness to boot.
Little Saigon: Thai/Vietnamese joint that sports two chefs, one for each cuisine. Reasonably priced and features nice, fresh fruit smoothies.
Two places that are a bit more like 'fine dining' (for Springfield at least):
Jimmy Oh's: fresh interesting presentations with an asian flair. http://www.jimmyohsrestaurant.com/
Ross Issac's which features lots of fresh seafood, but generally serves a seasonal menu...chef owned. The atmosphere is quirky and has damn fine drinks.
Kiku's is a new teppanyaki restaurant that has some excellent sushi to boot.
A bar in Chatham (5 miles south), Fat Willie's has a real good burger and has a real small town bar feel to it.
hope this helps, if nothing sounds good, give me some ideas and I can come up with a few more options...