I need to flash back to my stock rom for just a few minutes to get my GPS working again (http://code.google.com/p/cyanogenmod/issues/detail?id=2090&colspec=ID%20Type%20Status%20Version%20Model%20Network%20Owner%20Summary%20Stars%20Priority). Everything I read says I need windows to do this, is there a rom I can download and just restore it with clockwork mod?
http://goo-inside.me/evo/stock/ruu/ provides a straightforward guide, reproduced below, of how to revert to a stock ROM, and it looks like all you need is ClockworkMod. You probably want the newest Dec. 15th software linked on that page. Heed the warning!
WARNING! RUU'ing your phone will wipe all data on your phone, and if done incorrectly, can BRICK your device permanently! Performing an RUU entails completely wiping your user data, removing root, removing your custom recovery, and switching to the specified radio, hboot, and stock Sense ROM version that's in the file name.
- Download the UnrEVOked Forever S-ON tool and flash from ClockworkMod or Amon_RA recovery.
- Download ZIP file for whatever software version you want to restore to. Note that you may not be able to downgrade, depending on your current software version.
- Check MD5 (Windows: HashCheck, Linux/Mac: Use md5sum comand from Terminal).
- Rename file to "PC36IMG.zip" (ensure that you do not have file extensions hidden, aka, that the file is not now "PC36IMG.zip.zip")
- Place file on the root of your SD card.
- Boot into hboot by powering off phone, then holding down Volume Down and Power until you are taken to the white screen with the skating Androids at the bottom.
- When asked if you want to flash the file, press Volume Up to confirm. The remainder of the prompts should be self-explanatory after that.
Just to note: You can actually do this from any Sense-based ROM - it doesn't need to be "stock" and it doesn't need to be unrooted. The important thing is the dialer app, because Sense's dialer has the special ##GPSCLRX# code in it and the AOSP dialer does not.
Probably the easiest thing to do is simply to get a Sense ROM and flash it like you normally would either via ROM Manager or manually via your recovery. There's a stock (rooted) 3.70 here, but you could also use something like Fresh 3.5 or MikFroyo if you prefer.
If you want to actually go back to a stock and fully unrooted ROM, then Matthew Read's answer is a good explanation which doesn't require Windows (or a PC at all, really).