Right, cheaper things that have improved/helped or added enjoyment to your cycling life. my wife and kids are thinking christmas atm. my contribution:
pedros tyre levers
the ride journal
new crudcatcher

New gloves are one of my favorite new bike related things… 🙂

New grips

tinsy-good shout, which ones under 20?

Aldi gilets – surely the best biking bargain ever

SPDs ok they are 45p over budget but a very worthy upgrade if you haven't already 🙂
Comfy grips
Padded shorts

donk-good links!

coloured chainring bolts!

a proper allen key set.

Some Gore-Tex Army Trousers which, at that price, can be altered to suit your preferred cut…?

Endura road overshoes (good for off-road too, but their off-road specific ones just ain't as warm!)
Smart 1/2W light

Gloves any that you fancy whilst scouring the usual suspects, CRC, Wiggle, Stif.

I bought a pair of 520's yesterday for a £1 under your budget from CRC. And in WHITE too 🙂

Woolie Boolies!

im going to add nunn hydration tabs.

Minty Arse Lard

A Buff.

Park Pizza Cutter

🙂

+1 for;

A Buff
and Smart 1/2 Watt light (the rear one).

Decent chain oil?
(I couldn't find a link to the stuff I use but in the summer I was quite impressed when Tom put a bit of this on my chain, was actually really good (on the road mind).

Another for a buff & to carry in your pack – SRAM powerlinks.

has the park pizza cutter helped or improved your cycling life? ill forgive you as you are the admin and you provide this forum….
ill add STW forum, its free but like recreational drugs and cake rather addictive.

bike-specific tools e.g.

Dedicated pedal spanner
Decent cable cutters
Good quality allen keys

Bright pink Pedros Tyre levers: http://www.chainreactioncycles.com/Models.aspx?ModelID=10042

They are really good IME, and you won't lose them easily with that colour.

Muc-Off
Bike specific cleaning brushes
A decent MTB specific pump
Wind-proof headband to keep ears warm in winter
T-shirt base-layer
Multi-tool

There's a guide to MTB trails around that looks quite good too, can't remember the name unfortunately.

I know it's 27, but sub to singletrack? The gift that keeps on giving.

if you want tyre levers, go for the Lezyne metal ones for a tenner.

This?

Can't metal ones damage your rims if you're ham-fisted?

Rapha winter socks – lovely warm, comfy socks

gore skull cap

two pints of lager and a packet of crisps??

well it said cycling "RELATED"…..?

Another vote for a buff, cheap ones to be had on ebay and are just as good as the original.

Rsp astrum rear light, probably the brightest you will buy just cable tie it to the bracket as it can move, still a bargain at £12 upwards.

Again pedros tyre levers.
A good lube something like white lightning clean ride for me.
Endura or bolle esp glasses.
A neoguard
Prolink epx grease, top stuff just don't use it on yer seatpost!!
Ultrafire xpg torch, granted charger and batts is extra but worth it.
otileb medium mud racer saddle bag, top notch and fairly waterproof.

+1 for wollie bollys this time of year