Arguably the best CPU to go for is a QUAD-core, as the number of applications/games that support 4-cores or more will become mainstream. (Some info on muti-core CPUs click here_(computing)
For the greatest flexibility, build it yourself - but this could be a bit on the expensive side (would be cheaper than Cougar, Novatech, etc though).
If a self-build is not an option, consider the following:
• NON-gaming PC (upgradeable to gaming standard - see below)
Dell Inspiron 530 with a QUAD-core CPU, 2Gb RAM, HD 2400 Pro*, etc - DE-select the monitor: click here = 359 delivered, or £344 with cashback (click here)
• Gaming PC (roomier case with more upgrade options)
Dell XPS 420 with a DUAL-core CPU, 2Gb RAM, 8800GT graphics, etc: click here = £475, or £455 with cashback (click here)
Get 2GB RAM extra for either from click here = £25.84 delivered, or 24.30 with cashback (click here). I chose this particular RAM as it's cheaper than Dell's upgrades to 4Gb (i.e. £35-40), & is guaranteed to work.
If you get the 1st PC, you can add a 8800GT in the future without a PSU upgrade click here. However, anything more powerful & physically longer in size, you 'may' need to get a bigger case & more powerful the PSU. G
* For the 1st PC - HD 2400 support for 2 simultaneous displays (the 8800 will be fine too): click here & scroll down:
• Two independent display controllers
Drive two displays simultaneously with independent resolutions, refresh rates, color controls and video overlays for each display
• Two integrated DVI display outputs
- Primary supports 18-, 24-, and 30-bit digital displays at all resolutions up to 1920x1200 (single-link DVI) or 2560x1600 (dual-link DVI)
- Secondary supports 18-, 24-, and 30-bit digital displays at all resolutions up to 1920x1200 (single-link DVI only)