I've recently found an extremely easy way to root my LG Marquee:
1. In Settings > Applications > Enable 'Unknown Sources'
2. Download app attached to this post to your phone, and install it, or scan QR code to download:
3. Run the app, select SuperSU instead of Superuser (Superuser fails to work at times), then click 'Gimli' option, then it should say 'Root successful' or similar. Then if root successful, open SuperSU app, it'll ask you to 'update binaries', so let it do that update; once SuperSU binary update is done restart the phone; after that you can install Rom Manager, and do your thing!
- (Optional, but recommended) Install custom ROM - CTMod (the best for this phone yet). First, make sure you have Rom Manager (Clockwork Mod or similar) installed, and custom recovery flashed, then download CTMod for Boost Mobile or Sprint®* (both reported to work fine) to your sdcard, then open Rom Manager and make it install 'ROM from sdcard', and don't forget to do a full backup before doing that!
Download CTMod here (official page):
For more information, see source of this root app (Framaroot) on XDA developers (note that Framaroot works for other phones as well, for list of compatible devices see list via link below):
(Note: so far only versions 1.3 and 1.4.1 of the rooting app are known to work)
Good luck!!! Post here if it worked for you!
*Sprint is a trademark of Sprint.