| For print work, you really want Adobe Photoshop, though it doesn't come cheap at around £350 ($650 or so). It is the professionals tool of choice in many if not most web design houses, so you're safe in the knowledge that it fits the bill perfectly.
Alternatively, you could start out with a cheaper application such as Paint Shop Pro. A more light-weight program, but still very useful and more than capable of producing professional grade layouts. At only £70 (Around $120), it is a much more affordable solution, particularly if you're low on capital or require multiple licenses.
Once you get to the bigger stage, vector software such as Corel Draw will become invaluable too, allowing much more precise control over vector graphics such as logos. You may also wish to look into 3D modelling packages such as 3D Studio or Truespace. Again, these run into hundreds if not thousands per license, but if it is professional grade software you are looking for, these are the essential titles.
NB - I stand corrected on the pricing of Paint Shop Pro, and know where I need to purchase software from in the future! | 
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