Best to go online I would say.
I've used crucial.com for laptop memory.
I've also used http://www.mymemory.co.uk/ for memory cards, I think they do RAM also.
FYI, shop4memory.com and memoryc.com are the same company (based in celbridge), shipping is 'free' to Eire+UK on the shop4memory.com site, whereas you pay shipping on the memoryc.com site though the prices are cheaper! It's worth pricing up on both. You can also call to the shop in Celbridge.
I've used both versions of the shop in the past and had a good experience with pretty fast delivery.
folks,
I can recommend http://flexxmemory.co.uk in NI - I found them through ebay initially. Answered my query quickly regarding upgrade requirements for my laptop and my sisters. Memory delivered promptly.
I used shop4memory aswell and found the service excellent having ordered the wrong memory the first time (a bit DIMM, me), there was no problem returning it and getting the right stuff.
I got PC world to install a DVD RW , RAM and Hard drive . cost me 34 euro installation .
In my PC , it was diffficult enough to install ram , cos the slots are well hidden
Try www.7dayshop.com for the RAM. i have used them before and found them very cheap. they also have a memory configurator to ensure you get the correct ram for your machine.