It can be hard to navigate the guzheng repertoire if you don't speak Chinese. Below is a sortable table of some of the songs out there, alongside English-language translations. The best way to find recordings for these songs is to search by their Chinese characters on sites such as guzheng.cn and youtube.com. For recordings of songs, search under 筝曲. For sheet music, search under 曲谱.
I've also included a rough approximation of each song's difficulty in the "Level" column, going from 1 (simple) to 9 (complex), with "Performance" indicating a sort of level 10, and "Ungraded" meaning I don't have a number for them yet. Levels are based on the Central Conservatory of Music (CCOM)'s Chinese Instruments Graded Exams, and various organizations' published lists of songs that must be known to pass those exams. Different versions of the same song can be more or less complex, so expect to find variations that are easier or harder. If you have level information for any of the ones marked "ungraded" or you feel the grading numbers given to a given song are too far off, please send me an email and I'll make changes.
hkgz: Hong Kong Guzheng Players Association Exam Details
ZCA: Zimei Chinese Culture and Art Association leveling sheet
Zimei: Zimei Chinese Culture and Art Association Music Resources Listing.
CC: Carol Chang
qinguzheng: Qin Guzheng Progress Timeline
USC: California Youth Chinese Symphony Exam Song List
Chung, Chen, Kwok: Titles and translations pulled from the corresponding thesis, listed on the Bibliography page
Liang: Taken from works by guzheng master Liang T'sai-Ping