While I was in an electronics store ordering some bits for my case project I came across this
http://www.maplin.co.uk/media/largeimages/31867i0.jpg
It's got 44 LED's, of which 13 are 3mm (including blue/maybe white/red/yellow/green/orange/Bicolour and Tricolour, hyperbright variants)
a green 10mm, some odd shape and PCB mount versions plus a single and dual 7 segment LED display
11 5mm (same as above but I think some flashing as well)
If you're in the UK and you want some spare LED's or you just want to have a go at some LED mods this is a handy little kit, so I bought one (costs £8.00 inc VAT). For more info on maplins website click in the search box and key in "RS37", sorry I couldnt get a link direct to that page.
It's made by Kingbright so it's probably available through most electroncis retailers.
Thought I would post it here as many people of late have been posting questions about "what leds do I need for...." and this kit would probably cover all the types you'd ever need.
Also when you've run out the box then you've got a handy foam lined box for storing other stuff like old spare processors etc.