Return to the Palace
A great hack for Sonic 2 that brings back Hidden Palace Zone.

Mighty the Armadillo 2
A really good sprite hack -- play Mighty in Sonic 2!

Sonic 2X
Sonic X for Sonic 2. Play bad futures in Sonic 2.

Project Shadow
Play Shadow in Sonic 2!

Sonic 2 take 2
A large-scale hack for Sonic 2, by SaLuS.

Sonic 2 Ultima
A great hack, wide range of changes!

Sonic 2 XP
A great start to this hack, by Overlord.

More than a memory
Another Shadow-based hack, another great hack!

Shadow Adventures
A good pallette hack, by Rabid.

Angel Island!
A port of Sonic 3's Angel Island to Sonic 2!

Sonic 2: the Rabid project
The beginnings of a great graphical hack!

Sonic 2 remix
A good graphical hack by OrdosAlpha.

Jingle Bells!
The archive's first ever music hack!