Hey there, I'll give you what advice I can since I'm pretty new to the whole road bike thing. Two good brands for road bikes that I'm aware of are Giant and Trek, you can also look at Raleigh, not entirely sure what their road bikes are like but their MTB's are excellent. You should be able to find at least one bike from each brand easily under £500, as for parts, well those brands of bikes won't give you low quality parts, trust me :P I'll carry this on in another comment, character count >.

If any really, really experienced road cyclists happen to read this, don't knock the information I give 'cause I'm no expert, but I'm just giving the advice I have. If this will be your first road bike, when you have a go on it, don't be put off by the feel of the bike. It will probably be harder to control than other bikes you're used to or you might get a nautius feeling on it, I know I did, but after a few rides on it you'll be fine, it'll be like any other bike. Continued on next comment >>

My recommendation is to buy the bike from a proper bike shop, be it Halfords or your local dedicated bike shop. They can set the bike up for you, adjust the saddle and handlebars to match your size and give you advice on bikes in general. If you buy it from the internet, chances are, it's gonna arrive at your door in pieces leaving you to put it together which can be dangerous if you're not sure of what you're doing. Also, if you have spare money from your budget after buying the bike >>

With your spare money, it's probably wise to invest in a few things for your bike such as... Good lock, water bottle and bottle cage, puncture resistant tyres (usually about £25 a tyre), lights, helmet (if you don't have one already). Now, this depends if you have the spare money, if you don't, just make sure you have a lock, lights and helmet. Don't get a crapper bike just so you can afford the other things for it. Also, sorry to hear about your other bike, good luck and thanks for reading :)

Dear Seph I think you need to find a bit more Dosh. The Boardman bikes get consistently rated as best for a budget and the lower end model looks (note "looks") similar to the carbon race models, used at the highest level (e.g. Nicole Cooke): http://www.boardmanbikes.com/road/road_comp.html For this you need £650 + pedals, but you get what you pay for and it looks the part. It is still only shimano tiagra, but a pretty good buy for a racing style machine. 

Hi, Look, I know that this may be out of context for you, but have you considered a Raven Sports Tour (http://www.thorncycles.co.uk/ravensporttour.html ).  I realise it would cost a bit more than you had envisaged but with a good lock (I think shacke locks are the best) and with a bit of common sense where you leave it, the RST would offer you a lifetime of low-maitenence pure cycling pleasure. I own the Thorn out and out touring version, the Raven Tour. It handles magnificently I have never tried an RST but I understand it combines superb handling with real road bike speed. Common to both models of course is the Rohloff speedhub. Now, a the Rohloff unit alone would cost as much as you were envisaging for your whole bike but in my opinion there is just nothing to compare with it in terms of sheer feel and solidity and relaibility and precision - sorry for that, I sometimes get carried away on the subject of mechanical excellence - German excellence that is, but a direct descendant from British engineering ingenuity, so it is perhaps suffice to say that it does the job and does it well! ... Just an idea :) Cheers, Andrew

Mathew Giant FCR is a great flat bar road bike, alternatively I have a raleigh allez which cost about £500 and it is fine, I have no complaints. Dont let anyone tell you that a road bike is not sturdy enough for commuting, I commute 8 miles a day all year round and have only suffered one puncture in the last two years. 

check out  http://www.bicycledoctor.co.uk/faq_stolen.html so you are less likely to get the next one stolen [researched from online sources, police leaflets and my experience]