S&R are good but also also try:
http://www.snowlines.co.uk/
http://www.europaskilodge.co.uk/
http://www.ellis-brigham.com/
http://www.nevisport.com/
http://www.tackandski.co.uk/
http://skateandski.co.uk/
and for info:
http://www.skiclub.co.uk/
http://www.gregh.co.uk/html/Bookmark.htm
A check list for skiing (* = hire to begin with and nr = not required if hiring):
skis*
poles*
ski bag(*nr)
boots*
bootbag(*nr)
3pr ski socks
3pr technical grundies
2x thermal top
thin fleece
ski suit (unusual to find a one-piece these days but they're v. warm and, if you want to ski in all weathers make sure it's waterproof - many aren't!)
ski gloves
fleece gloves (if it's warm)
balaclava (stretchy TurtleNeck - wonderful)
sunglasses (on a string!)
goggles (for when the light's bad)
tiny rucksack (with no loops or straps)
water bottle (eg old pop bottle)
baby first-aid kit
whistle
compass
headtorch (no, I've not needed it yet)
plus usual outdoor clobber for off the piste.
Don't forget to get proper insurance - these people are good:
http://www.snowcard.co.uk/