I'll exclude my own problems, because I like all of them :)
800: 2057A - MEX Table
900: 2140B - Another Divisibility Problem
1000: 2162B - Beautiful String
1100: 2084B - MIN = GCD
1200: 2085B - Serval and Final MEX
1300: 2056B - Find the Permutation
1400: 2127C - Trip Shopping
1500: 2078C - Breach of Faith
1600: 2084D - Arcology On Permafrost
1700: 2109C2 - Hacking Numbers (Medium Version)
1800: 2155D - Batteries
1900: 2154D - Catshock
2000: 2096D - Wonderful Lightbulbs
2100: 2092E - She knows...
2200: 2155E - Mimo & Yuyu
I'll exclude my own problems, because I like all of them :)
One problem from each difficulty 800-2200
800: 2057A - MEX Table
900: 2140B - Another Divisibility Problem
1000: 2162B - Beautiful String
1100: 2084B - MIN = GCD
1200: 2085B - Serval and Final MEX
1300: 2056B - Find the Permutation
1400: 2127C - Trip Shopping
1500: 2078C - Breach of Faith
1600: 2084D - Arcology On Permafrost
1700: 2109C2 - Hacking Numbers (Medium Version)
1800: 2155D - Batteries
1900: 2154D - Catshock
2000: 2096D - Wonderful Lightbulbs
2100: 2092E - She knows...
2200: 2155E - Mimo & Yuyu