Special thanks to Michelle Natrop of the Minnesota Office of Transit for submitting the following info regarding noteworthy bikeways in her state (which I've supplemented w/additional info).

State Trail Overview Map (pdf file)

Mesabi Trail
132 mi (97 miles paved) rail trail that zig-zags up, down and through the Mesabi Iron Range, around piles of taconite tailing and ore, through pines and poppy fields with few houses and little highway noise.

The Gateway State Trail is a 18.3 mile long multiple use trail starting in St. Paul. This paved trail cuts through a cross-section of urban areas, parks, lakes, wetlands and fields in Ramsey and Washington Counties.
http://www.gatewaytrailmn.org/
http://www.dnr.state.mn.us/state_trails/gateway/index.html

The Heartland State Trail was one of the first rail-to-trail projects in the country. It is a 49 mile multiple use trail between Park Rapids and Cass Lake.
http://www.dnr.state.mn.us/state_trails/heartland/index.html

The Paul Bunyan State Trail will be a 110 mile long multiple use trail between Brainerd/Baxter and Bemidji. Currently, 74.5 miles of the trail is paved. The remaining 35.5 mile section is undeveloped with variable surface material ranging from the original railroad ballast to sand.
http://www.paulbunyantrail.com/
http://www.dnr.state.mn.us/state_trails/paul_bunyan/index.html
http://mnbiketrails4.1upsoftware.com/main.asp?SectionID=3&SubSectionID=17&TM=58091.75

The Willard Munger State Trail consists of 63 paved miles that connect Duluth and Hinckley. This trail also consists of the Alex Laveau Memorial Trail, a16 mile route that combines an off-road paved trail, and paved shoulders to connect New Duluth and Gary, and the Boundary segment, a 80 mile natural surface trail used primarily for snowmobiling, horseback riding, hiking and mountain biking.
http://www.munger-trail.com/
http://www.dnr.state.mn.us/state_trails/willard_munger/index.html

The Root River State Trail is a 42 mile long multiple use trail meandering through the quaint and picturesque rural communities of Fountain, Lanesboro, Whalan, Peterson, Rushford and Houston, and winding along the Root River on an abandoned rail bed.
http://www.rootrivertrail.org/
http://www.dnr.state.mn.us/state_trails/blufflands/root_river.html
MNbiketrails.com's trail description

Harmony/Preston Valley Trail
12 mile rail trail through hills, woods and tall grass prairie with great views; connects to the Root River Trail.

Lake Wobegon Trail is a 46 mile long, paved trail extending from the city of St. Joseph to the city of Sauk Centre. The trail also has an extension on the west side of Albany heading northeast to Holdingford.
http://www.lakewobegontrails.com/
http://mnbiketrails4.1upsoftware.com/main.asp?SectionID=3&SubSectionID=15&TM=58072.1

Midtown Greenway is a nonstop bicycle highway and walking path in Minneapolis parallel to and north of Lake Street. When completed, the Midtown Greenway will connect the Chain of Lakes with the Mississippi River.
http://www.midtowngreenway.org/

Central Lakes Trail
55 mi paved rail trail along I-94 in Central Minnesota.