does anyone know of a good sounding amp that is under 100 pounds?

line 6 spider 1x12. everything you need.

Fender fat strat
Ibanez s620ex1

Marshall MG250dfx
tech 21 trademark 60. it's also a 1x12, but has a really awesome tube-y sound. I've owned both the trademark 60 and a Spider, and I vastly prefer the Tech. Customer Service is great too.
actually, i didn't notice this before, but i'm gonna guess you're british. in that case the tech 21's out. i'm not sure what you could get for under 100 pounds sterling really...
i play most things from metal, to some funk, bit of punk aswell.
Depends what you will you use it for.

Will it be just used for practicing at home?

Do you want lots of built-in effects?

A Line6 or low-end Vox amp will give you plenty of different effects to play with but some people say they don't sound quite the same as an all valve type amp. But there isn't anything 'wrong' with them and offer a lot of value for money.

If you don't care for effects and just want your guitar's tone to remain intact, get a valve amp. They can be expensive, but Epiphone make a 5 watter that is a lot louder than you would expect for it's size. It produces a great classic rock 'crunch' sound when you crank up the volume.

So it depends what sound you want and if you just want an amp to practice at home with a Line6 Spider should be just fine. But if you are in a band or thinking of joining one it's worth considering a decent valve amp!
cheers man

i'm just hoping for a practice amp really, built in effects would be quite useful cause i would like to experiment with stuff.