This speadsheet compares the Globalsat DG-100, the Sony GPS-CS1 / GPS-CS1KA, the Qstarz BT-Q1000, the GiSTEQ CD111 and DPL700, and the AMOD AGL3080 GPS loggers.
UPDATE 2008-01-16: Public, published version of spreadsheet
I have also reviewed all of these models.
UPDATE 2008-01-29: Added and reviewed Holux M-241 (doesn't fit in table below, but it's in the Google spreadsheet). ENDUPDATE
UPDATE 2008-08-01: I will leave the old information below, but it is too complicated to maintain both the version below and the Google Docs spreadsheet in sync. Please refer to the spreadsheets link above, it is kept up-to-date and has more room as new GPS logger models are added. The version below is no longer maintained. ENDUPDATE
UPDATE 2008-01-16: I found GPSpassion.com also has done a spreadsheet, covering some other models
If you want more information, you can also check Amazon.com (USA buyers only)