There is no shortage of websites available for musically challenged preschool teachers. Try some of these teacher favorites for preschool song ideas:
http://www.kididdles.com/: This website has the melodies and lyrics to hundreds of best loved children's tunes. You can search by song subject, making thematic planning a breeze. There is also a link to printable lyric sheets. Build your music library by printing the lyrics to the songs you use the most.
http://bussongs.com/: Bus songs has a searchable database of over 2,000 children songs from lullabies to nursery rhymes and camp chants. You can search alphabetically, or by song subject.
http://www.kidsmusictown.com/ Kids Music Town has a searchable database of children's songs separated into 25 subjects including school songs, nature songs, and finger plays.
http://www.songsforteaching.com/index.html Songs for Teaching is a sister site to Kids Music Town and includes songs for every subject across the curriculum. The lyrics are available to view, and you can listen to a short clip of the song, but you must pay to download entire songs.
http://www.theteachersguide.com/ChildrensSongs.htm: The Teacher's Guide does not include as many songs as some of the other websites, but it does have a decent searchable database. You must know the song you are searching for before visiting this website, as the only way to search here is alphabetically by song name.