Do you mean stable isomers, or just isomers you can draw on paper?
1) Acetic Acid
2) Methyl formate
3) 2-oxoethanol (or is it 2-hydroxyacetaldeyde?)
4) 1,1-dihydroxyethylene
5) E-1,2-dihydroxyethylene
6) Z-1,2-dihydroxyethylene
7) ethylene peroxide? H2C=CHOOH
And with rings
7+1) (2R)-2-hydroxyoxirane (silly code converts the correct number into a smiley)
9) (2S)-2-hydroxyoxirane
10) 1,2-dioxetane
11) 1,3-dioxetane
Of course some of these are more stable than others...