You can normally get a good cheap set of the pantone swatch books from ebay.

The following links are to my US associate store so search on amazon if you prefer.
Logo Lounge (1 and 2). My two favourite books on my shelf. There is a third one just out but i dont have it yet. All about logos.

Why Not Associates 2. Fantastically creative design studio in the UK. My copy is falling apart from use

1,000 Greetings. Good for ideas on interesting mailshots, invites and material to hand out to people.

Designers in Handcuffs. Less design and more business design. Good for dipping in and out of.

Or getting some of the yearly annuals of the best of design is normally a safe bet. Although my preference are the ones that focus more on european design. I find american design a bit cheesy.

If i could afford it this is what i would be buying: D&AD: Buy - Publications