Edit: Ordered! (With time to edit though). Thanks for all your help guys. =)

I was determined not to post, but I've given up! So much has changed in the ...7 years since I made a desktop.

Looking for a motherboard to go with this system.
Have a £50-£110/$100-$220 budget left.
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Intel Quad Core Q6600 95Watt G0 Stepping £126.90 $253.8
Edit for future readers: UK buyers can get this cheaper on Overclockers

Corsair Twin2X 4GB DDR2 (2x2048MB) XMS2 Dominator 8500C5 5-5-5-15 £83.42 $167

Sapphrie HD 4850 512MB £128 $256 (heh, memory/price in £/price in $ all consecutive powers of 2)
Edit for future readers: UK buyers can get a cheaper 4850 on Overclockers (Gainward edition)

Arctic Cooling Freezer 7 Pro Socket 775 CPU Cooler £18.57 $37
ThermalTake Soprano Black Middle Tower Case £47 $94
Antec P182 Super Midi Tower Case £87.54 - Well worth the upgrade according to reviews. Worked with the case before also. Plus should last me a good 10 years unless there's some radical motherboard form factor change or something.

ThermalTake Toughpower 700W PSU £72.26 $144
Thermaltake W0103 Toughpower 600Watt ATX Power Supply £60 $120 (sufficient)

Edit: Chosen mobo;
Asus P5Q Pro - P45- £80.41 $161

Total: £584.77 / $1,168.78
Bit more than planned, but budget is quite flexible. (Especially if someone gets round to buying my MSDN subscription on eBay )
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I don't really plan on upgrading for 4 years, nor am I going to wait for Nehalem. I play a lot of games, and don't expect to be able to play the top end games 2 years from now in anything other than medium-low settings.

Edit:
If I do upgrade graphics it would be a while from now; so I am aiming for a cheap non-crossfire supporting P35/P45 mobo intending to replace the gcard later, rather than go with a more expensive X48 and upgrade later by adding another card.

Based on using a P35 or P45 chipset, I've narrowed my vendor's motherboard list to these candidates. (x48 boards too expensive when not using Crossfire)
--The list--
Asus P5Q Deluxe - P45 - £129.25 $260
DFI LANPARTY DK X38-T2R £123 $246
Asus P5Q-E - P45 - £108.90 $218
Asus P5K Premium - P35 - £107.35 $215
Asus P5Q - P45 - £97.53 $195
Asus P5K-E - P35 - £94.85 $188
DFI LANPARTY DK - P35-T2RS£87 $174
Asus P5KC - P35 - £86 $172 - Only one to support DDR3 also
Asus P5K Pro - P35 - £81 $162
Asus P5Q Pro - P45- £80.41 $161 - Chosen. Best out of all really.
Asus P5K - P35 - £72.79 $145

Twin x16 are not viable at my resolutions. Thanks shadowduck for that tip!

I already have an old SATA & 2 IDE hard drives as well as a dvd+-rw and don't plan on replacing them.

Thanks _so much_ in advance for any advice. I'm in way over my head.

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For the benefit of others:
http://www.novatech.co.uk/novatech [...] Q6600E#top - CPU
http://www.novatech.co.uk/novatech [...] REEZ7P#top - Fan
http://www.novatech.co.uk/novatech [...] P-4850#top - Graphics
http://www.novatech.co.uk/novatech [...] HX8542#top - Ram
http://www.novatech.co.uk/novatech [...] T-SOPB#top - Case
http://www.novatech.co.uk/novatech [...] -W0106#top - PSU

Look at something with X48- P5E Deluxe is a good call.

The P5E3 is a DDR3 board so avoid that one.

If you are running under 1920x1200 resolution you don't need dual 16x. Dual 8x on a P45 motherboard would be just fine.

Thanks for your reply shadowduck.
I am likely running under that res for the foreseeable future, so plan to use a single card at the moment and later either upgrade the card or add a second.

Narrowed list of boards down to just those that support DDR2, use P45/P35 and have onboard audio. Wrote the full list up so it's easier for people to point out ones to avoid/recommend.

I'm still confused about chipsets. Read loads of articles (most more than once :\) and still can't find a clear winner between p35/p45 given the cost differences. THG says P35 has faster usb/sata throughput and is better if building a new system, other comparisons say p45 "wipes the floor" with p35. Most bonuses apply to crossfire which I may not ever use. (I'm assuming by the time I upgrade ~2 years from now it's probably more viable just to replace the 4850. Still want opinions on that assumption though).

Thanks again all.

P45 is the newest chipset that replaces P35. P35 will be phased out.

Smart call on the video card- in 2 years you will want to just replace the video card.

P35/45 is really about the same. If you never plan to Crossfire go with the cheapest motherboard that meets your needs regardless of the cihpset. Both work well.

Excellent. Thanks again.

I think I'm going to go with the Asus P5Q Pro;
http://www.novatech.co.uk/novatech [...] U-P5QP#top
Interestingly, it's priced $30 cheaper than the "Asus P5Q" (no pro). Only down side compared to all the others (up to £120!) is a lack of eSata port (back connector provided and 6 onboard sata+2 drive expert), no dddr3 support (doubt it will be worth it), and no optical (which I never use anyway).

Think I'll use extra cash on getting a better case.

Look at the P5Q-E I think it has an eSATA port.

yes P5Q-pro, but skip the Reapers, they are having some problems on P5Qs. Check with Crucial, I think they have the most success on those boards.

Mmm. It's £28 ($56) more expensive than the P5Q Pro, which has a header + free backplate for an eSata port. Not as elegant perhaps, but good enough.

Cool. I'm actually going with the Corsair ram. The bracketed items were just the next models up by cost on novatech's webpage. Thanks for the heads-up though.