I just rooted my LG Optimus One P500 with Froyo 2.2 with a one-click application named Gingerbreak.
Download
1. First of all, you must download the Gingerbreak installation file from the XDA forums. Here’s the link: gingerbreak-v1.20.apk
(Ignore the message that says it’s incompatible)
Install
2. Open OI File Manager and go to mnt/sdcard/download.
3. Open gingerbreak-v1.20.apk from your list of downloaded files to install the application.
Enable USB Debugging
4. Go to Settings and then select Applications. Click Development and select the USB debugging checkbox.
Root
5. Open the Gingerbreak app and click Root Device. Your phone will reboot automatically when the rooting is complete. This will take a little longer than your usual boot up time but don’t panic! 
Finally, check for a new app named Superuser in your phone to confirm that your phone has been rooted.
Note:
Don’t worry if your SD Card has other stuff on it. Mine did too but nothing happened to them.
Ensure that your phone has enough battery charge to go through with this. Interruptions during rooting can cause problems.
If for some reason the procedure does not work, then turn your phone off and turn it back on before retrying.
If the app does not work,check if you have installed the app on the Phone memory and not in the SD card. Move the app to Phone if it’s on the SD Card.
You can now kick some serious ass with your rooted device! 
Steve Troletti
September 24, 2011 at 8:50 pm
Great blog post! To the point and worked like a charm. Thanks for the info!
Phoenix
September 24, 2011 at 9:40 pm
Thanks, Steve!
Ryan
September 26, 2011 at 5:52 pm
I think you have amazing site. i will follow this one. thanks
Homer
October 2, 2011 at 8:46 am
Lg P500 now starts in yellow screen emergency mode.. am i screwed ?
kenneth
December 12, 2011 at 7:41 am
yes u r screwed if u can only see emergenct mode
affan indonesia
November 12, 2011 at 12:09 pm
mantappp broww terima kasi banyak semoga sukses selalu….thanks for info ..its help full
apt2225
December 14, 2011 at 12:03 pm
I did all that said here..The phone rebooted after few minutes..But I dont see the Superuser app. Where will it be?. Am I missing any here?
Ray
January 23, 2012 at 8:08 am
Was unsuccessful with superoneclick and another method, but this one worked perfectly. Huge thanks!!
Linda
March 1, 2012 at 5:01 am
Thanks so much, superoneclick just wouldn’t work, but gingerbreak did.
gus
March 4, 2012 at 1:48 am
excelent work! very easy. Thanks!
Ramana Reddy
April 18, 2012 at 6:32 pm
Can I upgrade to 2.3.3 after rooting my LG P500 2.2.2 Froyo ?