I have played the guitar, at times professionally, for about 40 years. I have also taught a number of people how to play guitar. And I have pre-ordered Rocksmith. It occurred to me this morning that this game is going to give a lot of people a reason to go out and buy a guitar. That is not something you want to enter into blindly.
Rocksmith involves really playing a real guitar. So a novice Rocksmith player is faced with the same challenge as any novice guitar student - what guitar to get. The problem is that at the onset, you don't know if you will take to the new activity, and continue to play the guitar. The temptation is to hedge your bet by spending as little money as possible on a guitar, just in case it doesn't work out for you. But the mistake that many novices (more often their parents) make is to spend too little, and end up with an instrument that is simply not playable. In doing so, the novice never has a fair chance to find out if playing the guitar is a good fit.
There are a lot of solid-body guitars available for less than $200, but there is a problem... To get a guitar to market at that price level, and still make a profit, it is necessary to cut a few corners - most importantly with regard to labor. Most of the construction of a solid-body guitar can be accomplished by robots and unskilled workers. But there are certain finishing steps and adjustments, known as the "set up" that must be made before the instrument can be usable. They include leveling the frets, dressing the fret ends, and adjusting the neck angle, truss rod tension, and bridge. Those operations require a certain amount of skill, and are not done at the factory on guitars that are intended to sell for $120. This also applies to any guitar sold on TV by a guy dressed like Zorro, and guitars they sell at discount big box stores.
Rocksmith works by "listening" to the pitch of the notes coming from a guitar. That means the guitar you use must be capable of being tuned, and staying in tune. A cheap guitar, such as described above, simply will not work. Not only will the guitar not play in tune, it can be difficult or even impossible for a novice (and often a professional) to finger all of the notes needed. Also the "I can always trade up later" argument does not work. Music retailers will not accept instruments in that price range for trade-in or consignment.
The publishers of Rocksmith are offering a bundle for $199 that includes a guitar - in other words, a $120 guitar. There is always a chance that they worked out a deal with Gibson whereby the guitars will be made playable prior to shipment. If you are contemplating that route, I suggest that you wait until a few days after the product starts shipping, and read the reviews.
So what do you buy? Your best bet is to move up-market just a bit. Starting at around $225 on-line and at music stores, you can get a guitar in Fender's Squier series that will fit the bill. And there are other brands in the $200 to $500 range that make excellent student instruments. You may still need to get some minor adjustment done, but you will have something you can actually use. At music stores, all the guitars they sell are set up to be playable.
What about that guitar in the attic that Dad has had since high school? You may have something very usable. But count on taking it to a local music store for re-stringing and adjustment. Plan on spending $30 to $100.
Speaking of strings, they will occasionally need to be changed. If a guitar is in storage, electric guitar strings become useless after about 3 years. For the purpose of playing Rocksmith, you can probably count on about 50 hours on a set of strings.
You may want to avoid acoustic-electric guitars. These are hollow-body guitars that just happen to have an electronic pickup. Some of them are great instruments - I own a few myself. But using one for Rocksmith means that you will hear the sound coming from the guitar at the same time as the sound coming from your gaming system. That could be a bit distracting.
One last thing. Regardless of brand, the majority of electric guitars are built to resemble either a Fender Stratocaster, Fender Telecaster, or Gibson Les Paul. The Telecaster-style and Les Paul-style guitars generally have the connector for the input cable at the bottom edge of the body. This is not a problem unless you intend to play sitting on a couch. Doing so is uncomfortable, and can cause damage to both the guitar and the cable. Unless you plan to do all of your playing standing up, go for a Stratocaster-style instrument. They usually have the connector on the front of the body.