REALLY tough to pick even just a few... since the thread says "songwriter", I will avoid people who are classified or who I think of as composers (that really would be a whole different list):
- Benny Andersson (would also make my composer list)
- The Gibb Brothers (particularly Maurice & Barry Gibb)
- Burt Bacharach
- Stevie Nicks
- Lisa Dalbello (one of the MOST under-rated singer/songwriters that I know... I even made a fan-page for her:
dalbello.4x2.net. I have always heard she was a big inspiration for singer/songwriters like Alanis Morissette)
- Christine McVie
- Per Gessle (the guy has an incredible penchant for writing simple pop songs, but somehow always with never-ending originality.. check out his solo stuff outside of Roxette!)
These are just the first to come to mind... there are so many excellent songwriters.