Timing belt
There aren't a lot of common problems, the vtec engines are very strong. Mine has needed since I got it a few months ago:
- new ignition switch. Was cutting out intermittently, £75 for the part and some scuffed knuckles fitting it
- air con leak repaired - about £150 including the part, diagnosis and regasses. Turned out to be one of the pipes which is prone to leaking
- juddering clutch - a poor/stiff/juddering clutch isn't uncommon due to having separate fluid that a lot of people wont bother changing (as opposed to using the brake fluid). A fluid change improved mine hugely but it will want a new clutch eventually.
It has also just failed the MOT on a leaking shock (surprisingly expensive part at about £90) and binding brakes, which should just need the calliper freeing up. Don't think either of these are especially common, merely part of the territory with cars this age