Check this
site out for details on all modes of transportation in Las Vegas.
FYI the airport shuttles are great! Very cheap, and pretty quick... plus, travelling on the shuttle gives you an opportunity to check out, what's where... and near your hotel.
Personally, I'd stay away from taxi drivers there...
We made a mistake of taking a taxi from hotel BACK to airport - guy tried to overcharge us...
We gave him money + tip, he claimed that money we gave was only enough for fare + 'airport charge' - we said that if there was an airport charge, it should have been clearly displayed in cab, or included in the 'extras' fee on the meter. He then demanded that we give him more money for tip. We stood our ground, and refused to pay anything more... as soon as we asked him for his taxi licence number, so that we could lodge a complaint with his taxi firm, he suddenly shut-up and jumped back into his cab.
Also, be weary of the cabbie that drives you 'all-around-the-world' to get you to your destination... they'll try anything for a few extra bucks!
If you want to go the taxi route, regardless, check out this
article for some tips & advice on getting a cab in Las Vegas.