Just to clarify, you have a pleco in the 100 liter tank and are also wanting to add one angelfish (please correct me if I am reading this wrong). I am no good with liters so I converted this to gallons, so your tank is around 26 gallons.
That being said some of the following would go nicely with the angelfish. As a side note do not get to small of fish or your angelfish will eat them once they reach adulthood.
- Cory Cats
- Black Skirt Tetras
- Lemon Tetras
- Platies
- Swordtails
As a rule of thumb if it is not a fin nipper, does not move really fast (danios are probably going to stress the fish out), and is bigger then an adult angelfishes mouth (these fish can get up to 6in.) then it will probably be okay.
The only issue I see is that your tank might be a bit small for the Angelfish once it is full grown.
What types of fish do you like?