Air Filters?

good evening people,

I'm after some info on air filters, are they any good and do they give the bike more power like on cars? I'm happy with mine so far even though i don't get to ride as much as i like too (misses problems) but I'm looking to add a few small things to her this year.

 

thank you for the reply, i'll have a look for some on eBay. iv always used k&n but wasn't sure if they was any good for bikes