Lets start with some links to maps.

the first map resource you should be interested in, as a player of e+, are those which are currently on, or have been 'seen' on the community servers, you can find access to current/previously played custom maps (through the ftp link) which can be found here : http://www.excessiveplus.net/blogs/easy/missing-maps

Many other maps can be downloaded from the following links.

http://download.pwnoogle.com/

http://www.fmj.q3.free.fr/Maps%20&%20Maps%20Packs/

http://b1shop.ahau-kin.org/maps/basewsw/

http://files.unlagged.com/quake3/baseq3/

http://www.keksfabrik.eu/gaming/q3files/maps/

http://databaseinfo.org/axiom/q3a/Maps/

http://q3a.ath.cx/

http://tcpm.mrlazyinc.com/files/maps/Quake%203/

http://www.whodah.com/Quake/index.php?dir=Files%2F

http://jocke.furver.se/q3a_maps/

http://neytrino.com/q3maps/

http://dl.q3files.com/

ftp://95.130.10.38/baseq3/

http://www.gamefront.com/files/listing/pub2/Quake_3_Arena/Maps_Levels_Missions

http://kubus.rulez.pl/files/index.php?path=q3/maps/&sort=name&order=asc&start=100

NB. some maps are in zip format, which will need extracting before placing in your baseq3 folder; some will download as example.zip but will need renaming to .pk3 format.

Tip: look inside the .zip file and see the file structure, if it contains a .pk3 file, extract it, if it contains a series of folders, rename it.

more resources coming soon...