The forums are full of releases of useful model packs, here's a selection of just some of the most recent ones:
The Driver Pack
The Driver Pack by
Superfrog and
Mosquito is a pack containing Team Fortress 2 themed ATVs (for both teams) and two weapon models: a mine and a lug wrench.
Download it here:

Check out the
forum thread for more information and to get support.
STARS Bravo Team
The STARS Bravo Team ragdoll pack by
dsdxp is a port of the models of the said team from the game Resident Evil.
Download it here:

Have a look at the
forum thread for more information and to get support.
USS Voyager
ApwnInTheDark's USS Voyager model packs are a port of various Star Trek models from the games Star Trek: Elite Force and Star Trek: Legacy.
Download the pack with the Voyager model, the Voyager Bridge model and the Shuttlecraft here:
Download the pack with the spacedock model here:
And have a gander at the
forum thread for more information.
Vault 101 Security Team
bloocobalt's Vault 101 Security Team pack is a pack of Fallout 3 models ported to Source that have been given the heads and skeletons of Half-Life 2 citizens.
Download the pack here:
Get the physics upgrade here:
And get the bodygroup changer here:
It is recommended that you download all of the above for an optimal experience.
And have a look at the
forum thread for more information.
GTA IV Comet, Minivan, and Stallion
This pack by
A big fat ass (otherwise known ad DrDeanDarko) is a port of three vehicles from Grand Theft Auto IV.
They all have multiple skins. To change them, follow the creator's description here:
How to change colors
<ul> Look at the vehicle you want to change colors
Go into console (~) and type ent_fire !picker skin X
Replace X with desired number (1 to 6 I believe.)
Download it here:

Be sure to give the
forum thread a look if you need more information or support.
Be sure to keep you eyes peeled for more model packs![...]