Unfortunately, asking for a guitar just isn't that simple. Apart from considerations of colour, size, electro or not electro, there's body style and shape too...
Don't worry though - here's a brief Normans Guide to the most popular you'll see to help you choose!
Dreadnought
The most common and most popular shape, the Dreadnought takes it's name from the huge battleships being built in Britain around the turn of the 20th Century in the lead up to World War I. The shape was first built by Martin in 1916 and has been copied by nearly every other manufacturer since. Characterised by square shoulders and bottom, the Dreadnaught offers a bold tone and impressive volume, factors which have insured it's popularity as a 'do anything' guitar - at home with any style, in any setting.
Famous Players - Johnny Cash, Elvis, Paul McCartney.. pretty much everybody!
Budget - Rocket SW203
Intermediate - Yamaha FG720S
Advanced - Tanglewood TW115 AS CE
Jumbo/Mini Jumbo
The Jumbo (originally called Super-Jumbo) guitars all started in 1937 with Gibson's J-200. A huge body makes for a deep, booming bass and some sparkling trebles. Not great for picking, but probably the world's best rhythm guitar.
Mini Jumbo guitars follow the same body shape, but true to the name, they're smaller in size. This allows them to be a little more versatile with picking but still retain a position as a credible rhythm.
Famous Players - Pete Townsend, Bob Dylan, Noel Gallagher
Beginner - Rocket SA-40 Mini Jumbo
Advanced - Tanglewood TW155 AS
Auditorium
The Auditorium arrived in 1929, the first flat-top 14 fret acoustic ever made. It shares alot with the smaller Grand Concert size and is becoming increasingly popular. Similarly to the dreadnought, it's gaining a reputation for being a real 'do anything' instrument, though it's perhaps most at home with Folk, Rock and Blues. Quite often seen with a cutaway, as on the left, they're also very popular as electro-acoustics. The shape makes them easy to hold and they don't carry the weight of the bigger Dreadnoughts, which make them an ideal choice for someone smaller or for someone (like me!) who doesn't want the bulkier shape. For those that do want a bigger sound, the Grand Auditorium shape offers an increased size.
Famous Players - Taylor Swift, Eric Clapton, Woody Guthrie
Beginner - Lag Tramontane T66A
Intermediate - Tanglewood Evolution TSF CE BL
Advanced - Yamaha CPX700II
Grand Concert
One of the smaller and lesser seen shapes is the Grand Concert. Ideal for folk, blues and old fashioned Americana music, the Grand Concert has been in production since 1877. A well built example will give clear, sweet middle tones, but lacks the power of the shapes above in the bass or treble. It's smaller brother, sometimes called the 'Parlour' guitar, shares the same specifications but has a smaller body, so volume and bass are reduced slightly again.
Famous Players - Joan Baez, John Mayer, Ian Anderson (Jethro Tull)
Advanced - Tanglewood TW170