I went with a 04 for the same (tax reasons) but the first thing I did was a £300 set of LED rears, as above, that's 2 years worth of tax, but then again you will have spent 1-2k more on the car initially, swings and roundabouts.
There's a thread in here somewhere about things to look for, but from me, check the rear axel doesn't click, and open the bonnet and move the rubber strips on the actual bonnet, make sure there is no bubbling under there as it can migrate through the metal and ruin the bonnet.
Get whatever you buy on a test drive over some nasty pot-holed roads to hear any odd noises from the suspension, banana arm bush failing are common but very noticeable over bumps.
Check for good brand tyres on all 4 wheels (preferably the same brand and model of course, but at very least, same brand over an axle), budget tyres may indicate the car hasn't been looked after in other areas too.
And if you can afford it, get the car checked over by an AA guy, could save you a fortune in the long run and any honest seller/trader wont have a problem with you doing this, if they reject, walk away as there will be something theyre hiding!