Is not easy! I upgraded my 17″ MacBook Pro to a 200GB 7200rpm drive, which gave me TONS of space, and it didn’t really matter what applications I installed or how much stuff got added in the form of data.
The second part is not as easy to solve and it largely depends on what you do – an accountant may be generating tons of Excel workbooks and PDF documents, while someone else *cough* could just be browsing RSS feeds and watching YouTube videos, and only touch Excel on ocasions.
In terms of apps, I was accustomed to large-size tools for my needs (coding web pages and PHP backends in Dreamweaver, PDFs would be edited in Acrobat, Photoshop would fill the graphic editing needs every now and then…). Here is a small table comparing various apps from the CS3 suite and some (admittedly not as powerful) alternatives:
Image editing: Photoshop (490MB) versus Pixelmator (113MB).
Web design: Dreamweaver (366MB) versus Coda (52MB).
PDF editing: Acrobat (832MB!) versus PDFPen PDFClerk Pro (12MB). I was going to mention PDFPen but after trying it and seeing how they totally ignore mouse input (you cannot use your mouse’s scroll wheel to browse through the PDF’s pages!!!) I’ve concluded it sucks.
These three apps alone are saving me 1.5GB of disk space without even starting to generate data!
Additionally, nothing like video or audio editing tools should be even installed, let alone used on this machine, as it’s drive only spins at 4200rpm, and basically grinds your system to a halt during drive-intensive tasks (such as opening or saving huge video files).
Another tip is to move as much of your data online as you can. Either using .Mac or a different free alternative, online music streaming, Flickr for photos, and so on – it will save you a ton of space.