1. Grimsby. March 1985.
2. Newport. April 1988
3. Rochdale. February 2001.
4. Lincoln City. March 2001.
5. Cambridge. March 2002.

Other answers:
Mansfield - played them in the FA cup 2 years ago.
Northampton - played them in the League cup in 2012.
Macclesfield - FA cup tie in 2013.
Wycombe - 11th in the list, last played them in April 2003.

Since our last game against Grimsby, there are 10 teams that we had never faced up to that point but we have since played in the league. These are:

Burton Albion
Milton Keynes Dons
Kidderminster Harriers
Macclesfield Town
Barnet
Maidstone United
Scarborough
Tranmere Rovers
Rochdale
Hartlepool United