Aside from the official L4D maps currently on servers #1 and #2:

WM_part2_v004
city_minami_department_a1
city_minami_street_a1
keltern_minates_house
l4d_Assault
l4d_cottageofdoom_b1
l4d_deadcity01_riverside
l4d_deadcity02_backalley
l4d_deadcity03_bridge
l4d_deadthoard01_prison
l4d_deathboard02_yard
l4d_deathboard_03_docks
l4d_dem_hospital01_apartment
l4d_dem_hospital02_subway
l4d_farm_of_death
l4d_hangumhigh
l4d_nkpit
l4d_nova
l4d_orange01_first
l4d_orange02_second
l4d_orange03_third
l4d_orange04_forth
l4d_orange05_fifth
l4d_resort04_beach
l4d_townsquare
l4d_alttp01_dungeon
l4d_billys_farm_b7b

vs maps

l4d_vs_minami_highway_a1
l4d_vs_minami_street_a1
l4d_vs_cottageofdoom_b1
l4d_vs_deadcity01_riverside4
l4d_vs_deadcity01_riverside8
l4d_vs_deadcity01_riverside9
l4d_vs_deadcity02_backalley
l4d_vs_deadcity03_bridge
l4d_vs_deadthoard01_prison
l4d_vs_deathboard02_yard
l4d_vs_deathboard_03_docks
l4d_vs_hunter_city_b1
l4d_vs_orange01_first
l4d_vs_orange02_second
l4d_vs_orange03_third
l4d_vs_orange04_forth
l4d_vs_orange05_fifth
l4d_vs_resort04_beach
l4d_vs_stronghold
l4d_vs_zelda01_d
l4d_vs_zelda01_f
terrain6

If you want to download these maps then google is you friend

Beware, many of these maps are crap. I particularily dislike the orange ones, which are indeed just orange textures everywhere

Any that you would recommend downloading?

honestly haven't played that many - there aren;t that many maps out there (since there's still no SDK) so I've pretty much uploaded all of the ones I could find to multiplay.

If I was going to have a play I'd probably look at deathboard and deadcity (remember to download the campaign maps - as there are versus maps available too that are slightly different)

orange textures lmao

are the zelda maps anything to do with the zelda games, or are they just lablled that for some random reason...

dunno, they're ones I've not tried to play yet