At KrazyDad you can not only find plenty of Slitherlink puzzles but also Penrose Slitherlink puzzles using the quasi-periodic 5-fold tiling discovered by Sir Roger Penrose. Each booklet contains six big Slitherlink puzzles in pdf format, with the answers in the back.
There are already 100 booklets, each with six Penrose Slitherlink puzzles, in easy printable pdf format available. Each book contains an assortment of difficulties, starting with two easy puzzles, then two intermediate, followed by two tough puzzles.
The rules summarized:
1. Fill in some of the dotted line segments to form a meandering path that forms one single loop.
2. The single loop of lines is to be formed, without crossings or branches.
3. A number in a cell indicates how many lines that must surround the cell, while empty cells can be surrounded by any number of lines.
Thanks to KrazyDad for bringing a nice variant to Slitherlink, one of my favorite puzzles !