Fallout: New Vegas companions

Companion wheel
The companion wheel is a new feature that is added to Fallout: New Vegas. The wheel provides easier control over non-player companion characters in the game.

There are 8 sections on the wheel, each with a specified function.

The available orders are:
 * Toggle melee/ranged fighting
 * Open inventory - This displays the companion's current inventory, inventory weight, and weight limit.
 * Toggle stay close/keep distance.
 * Back up.
 * Toggle aggressive/passive AI.
 * Use stimpak.
 * Toggle wait here/follow me.
 * Return to normal dialogue.

Permanent companions
You can have up to two companions, one humanoid and one non-humanoid. All companions default weapons have unlimited ammo.

Humanoid companions

 * Arcade Gannon, a member of the Followers of the Apocalypse with a mysterious past. He can be found in Old Mormon Fort.
 * Craig Boone, a very-talented Ex-NCR sniper with a grudge against Caesar's Legion. He can be found in Novac.
 * Lily Bowen, a friendly nightkin and former member of the Master's army. She can be found in Jacobstown.
 * Raul Tejada, a ghoul mechanic and former gunslinger held hostage by Tabitha, the mad leader of the State of Utobitha. He can be found in Black Mountain.
 * Rose of Sharon Cassidy, a caravan merchant and the daughter of John Cassidy. Also known as Cass. She can be found in Mojave Outpost.
 * Veronica Santangelo, a disillusioned Brotherhood Scribe. She can be found in 188 Trading Post.

Non-Humanoid companions

 * ED-E a prototype eyebot designed for combat and reconnaissance operations. It can be found in Primm.
 * Rex, a cyberdog belonging to the King. It can be found in The King's School of Impersonation.

Temporary companions

 * Neil, a disgruntled super mutant.
 * Sunny Smiles
 * Trudi
 * Deputy Beagle
 * Private Halford
 * Victor

Companion lost (console/360)
Companions may sometimes disappear, while playing i lost Veronica Santangelo, but several quests later she reappeared for some reason mid-way through the quest "there stands the grass", i have recently lost the companion "ED-E" after completing the quest "guess who i saw today", and i hope he will return in the same mysterious fashion.

Companion Lost (PC)
Lost your companion again? Told one to wait for you - and forgot him (or her - don't tell your lady companion to wait for you and then forget her, that is kinda rude) Or is your companion stuck in a cell? If you play on an Xbox or PS you are out of luck. (and you paid about 30% of your currency more than if you bought it for PC) If you play on the PC on the other hand, basically this is all you have to do:

for ref_id have a look at the companions page on this wiki, the last row of their Character-Box usually states their ref-ID.

To get the console up and running have a look at the Console Commands

You can use (instead of both commands stated above) too - if you want to know where you lost your companion and feel lucky. In other words: save the game before you do this - it might save you some frustration.