Suggestion, apologies if already mentioned or it already does and i've just not noticed:
A 'system basket' that sorts your basket into typical system elements such as CPU, Motherboard, RAM, etc. etc. so for people building a system it makes it nice and easy to see what you've got and what you may have forgotten.
I've done it plenty where i've specced a machine to a budget and then realised I did something daft like forget a hard drive in my excitement at choosing graphics cards and then have to slash £50 back out the spec to fit it in.
I know at least one of your competitors do this and it's a fantastic feature IMO.
Presents an opportunity to encourage more sales too as people will look at the typical components, see a section empty and think 'Oh, I hadn't thought about a sound card' and maybe end up adding one in fo example.