This is just by way of collecting a few pointers to stuff I think is currently A Good Deal, and passing comment that fifteen years ago I was principally working with machines that only had 1.6Mb floppy disc drives...
Prices include delivery. Obviously they'll change over time and new products get substituted, but always remember to factor shipping into any "bargains" spotted online (eBay is rarely competitive for stuff like this, as the sellers have often been sitting on stock and are trying desperately to recoup those costs.)
Also obviously: check around before buying. These are just pointers.
DVD.co.uk are selling 2Gb flash drives for £11. They (and Amazon.co.uk) had 4Gb drives for £18 a while back, but it seems the stock at those offer prices has been cleared, so they're back to £25 at present. Keep in mind that Amazon's free shipping doesn't kick in until you're over fifteen quid. We might not get another good price drop until 8Gb drives become common.
Play.com want £7 for a spindle of 50 CD-Rs. SVP.co.uk usually have DVD-Rs in their bargain shipping category, with a 50 spindle for under £10 all in. I doubt these prices will fluctuate quickly as double-layer DVD blanks haven't taken off. Data HD-DVD drives will be a long time coming at affordable prices.
500Gb external USB2 harddrives (Western Digital My Book brand) are £90 from Amazon. Doubtless they'll come down a fair chunk when terabyte drives arrive commercially in number. Terabytes of data storage? Ack. See opening sentence about starting off with floppy-only machines.
If you're storing stuff you don't need to access quickly, 200Gb of discs on a spindle may be a cheap, practical alternative to an extra drive.
Might update this post later and change the dates as necessary.