Of the places I have been:
Minnesota - much better experience with TCF than the dreaded Metrodump, but the Gophers are still working on developing a game atmosphere; it will take time. The UW Alumni Club of the TC closes off a block in downtown Mpls for a pre-game party (in front of Rozens) which is very cool. They also had buses to TCF or you could walk. TC is a fun place to visit (of course, I lived there for three years so am a little biased). We go every year.
Columbus - The Shoe is incredible. I also had no problem with the fans, but then I was in a group. Learn the alternative lyrics to the Michigan Fight Song and you will have friends everywhere. I've been here twice and would go again. Like the stadium better than PSU, but PSU fans were slightly nicer. Close call between the two. Lots of locals, some with severe dental issues, show up for the games. One guy I was talking to said "Yeah, on gameday some of these folks come down out of the hills and they scare even us." Most "southern-feeling" of the places I've been in the Big 10.
Penn State - Great fans (even though someone stole Monsignor's Badger jacket from a chair outside our RV), but it's a pain in the butt to get there. We drove to a little town about half an hour away, rented an RV there, and stayed in the RV on their tailgating lots. I think you can also rent an RV already set up on the grounds and just drive up to that. We may try that next time and then fly to Harrisburg and rent a car (as I get older, comfort trumps cost). Stadium kind of looks like an erector set, but it is rocking. Would go more often except for you-can't-get-there-from-here.
Northwestern - Best thing about going to a Northwestern game is that it is in Chicago. We have a friend who lives in Evanston, within walking distance of the stadium, so we have a nice spot to tailgate. Their stadium renovation a few years back made it much more fan-friendly. Local fans are apathetic, at best. Easy visiting team ticket. I kind of like the stadium in a small-liberal-arts-college kind of way. The kitty-cat roar is annoying (ditto for PSU). Pre-renovation, was named Dyche Stadium (now called stadium formerly known as Lesbo) giving rise to comments like "You'd think a place called Dyche Stadium would have more women's restrooms."
Iowa City - Get hotel rooms early (like February). Nice town, have old friends who live there, kind of an old-hippie ambiance. Tailgating is scattered except for one big lot, but fun. Similar to Wisconsin, if you show up at a tailgate with a 6-pack and a decent attitude, people will be glad to talk football. Lots of stands selling those big-ass turkey legs. Stadium renovation helped women's restrooms, but now the men have a line. Concourse not laid out particularly well (this is true of upper concourse at Camp Randall too) and visiting fans get horrible seats (same at the Camp). Always enjoy IC - it's like visiting the cousins you only see every other year; hard to work up a hate.
Champagna - Illinois is a basketball school, but they try. If you can, drive down and back the same day. Most hotels have two-night minimums and one night is more than sufficient in Champagna. Tailgating lot is good; people were friendly; only seemed to be a couple of downtown bars, but there were some decent restaurants. Been there twice, but would only go back for a big game. Stadium renovation was half done when I was there, but it looks like a good one. Impressive facade to the stadium.
Going to Michigan this year for the first time. Haven't done any of the Indianas or MSU.