Adding RAM is the fastest, easiest, most cost-effective upgrade you can make for Pro users. And you should consider putting 1GB modules in all the slots and going to a more studly 8GB, and just selling off the leftover 512s on eBay.
Picking up a couple of hardware utilities like TechTool or Cocktail to handle some maintenance tasks will help keep the machine happy.
Another useful upgrade is adding another drive into an available bay if you have one. Photoshop and Illustrator do like to have a honking great chunk of disk elbow room for their history, cache and redo/undo features, so more room for scratch disk operations is helpful.
You may have noticed that Firefox is a terrifying RAM hog, since web browsers are now expected to do so much more than read HTML these days. (Note 462 MB for FF vs 255 MB for PS and 176 MB for Illustrator!) One helpful trick is to add the Flashblock plug-in to Firefox, will ease both it's RAM and processor footprint, by only running the Flash objects you choose to enable. (You get a click-able [F] icon instead of downloading and running the Flash bits automatically) But even then, you still should close and relaunch Firefox to reclaim the memory and clear it's cache regularly. You might consider leaving it off if you're not using it while working in Photoshop and Illustrator.
As for the BIG upgrade - that's a toss up. I'm not impoverished, but tight - so still using a (quite pampered) G5 Tower, but that will not run CS5, which requires an Intel processor. And of course so does Snow Leopard and Lion... and you need those to get the Mac App Store, so modern apps are beginning to drift out of reach... So I live in mild fear of getting the CS5 file I can't open in CS3.
For those of us facing upgrades, we have to consider the non-trivial cost of a Mac Pro and Display and it's studly speed, build quality and expandability, versus the not-at-all-shabby performance of a i7 27" iMac.
Mac Pro (2010)
A current Mac Pro (Yes sandy bridge/thunderbolt upgrade on the eventual horizon...who knows when... ) the base model, modestly configured: 2.8GHz Quad-Core Intel Xeon, 8 GB Ram, 2 1TB Hard Drives, ATI Radeon HD 5770, Apple LED Cinema Display ($999) , iWork, MS Office, Applecare weighs in at a hefty-
$4,539.95 US
iMac (2011)
A
maxed out iMac, similarly configured, (2011 Sandy Bridge gen): 3.4GHz Quad-Core Intel Core i7, AMD Radeon HD 6970M, 8 GB Ram, 2 TB HD, iWork, MS Office, Applecare is a bit more reachable at -
$3,016.95 US
The price difference here in the states is $1,525, and probably even more dramatic for you UK chaps. In Apples (and Intel's) defense a 2.7GHz Xeon is still heavier iron than the 3.4GHz i7, even a generation back. But that's still totally smokes my relatively ancient kit.
That's enough to pay for the CS5.5 Upgrade
AND an iPad... with a little change.
That's what Graphics Pros are facing. We'd love the expandability and maintainability of a tower, but our budgets have been tightening. Don't get me started on glossy screens...
Your mileage may vary. Banzai.
