Champaign-Urbana, by itself, isn't a very easy place to watch trains. The downtown depot's platform is open only to ticketed passengers, though you can get a pretty decent view of all rail traffic as passes the Champaign Police Department's parking lot on 1st street. CN/ex-IC is the dominant player here, but as previously mentioned, Amtrak comes through as well. CN's yard is in a bad area of town and viewing of it isn't possible from any good spot without trespassing. Better left alone. NS runs a local through Urbana a few times a week, but I've seen it only a handful of times. It runs usually with one loco and a short string of cars.
If it's frequency you want, you'll want to head out of town a few miles. Tolono is 8 miles south of the twin cities and features a diamond of the CN line with NS. Viewing is pretty good there, though railroad employees aren't too fond of people walking on or too near the tracks. Probably see 50+ trains here per 24 hours, which is better than anything else within 30 minutes of C-U. Tuscola's diamond may have similar totals per 24 hours, but in my experience there, that location is either hot or dead. Tolono seems to stay pretty steady. Route 45 is a good one for pacing trains in that area between the towns. Sidney has both UP and NS running through, crossing each other just east of town.
Send me a personal message if you'd like more detailed info.
