Soccer matchs in Europe

It's very difficult to get tickets for Liverpool and Chelsea matches. Tickets are typically only sold to "members" of the club. I usually go to the stadium on the day of the match, and try my luck with the scalpers/touts. But for high-profile matches sometimes the scalper are just buying tickets instead of selling.
I haven't personally used them but I know some people who have been satisfied with: http://www.thomascooksport.com/Football.

They sell ticket/hotel packages.

Milan and Barcelona matches are a bit more easier to get tickets to:
Head over to their website for more details:

https://entrades.fcbarcelona.cat/web/en/entrades.html

http://www.bestticket.it/newbt/default.asp?shop_id=MILANENG

For Champions League matches in Italy I've been happy with this travel company which does ticket/hotel packages:

http://www.findyourevents.com/catalog.aspx?type=2&id=1

Just to let you know that "ticket touting" (scalping) is illegal in the UK. This site sets out the law which was put in place to, amongst other things, cut down on crowd violence by keeping opposing fans apart and prevent individuals banned for violent behaviour from entering football grounds.

http://www.homeoffice.gov.uk/documents/football-ticket-touting?view=Binary

There is also the very high risk of buying forged tickets.

Touting is illegal in most countries around the world. In my experience, the practice appears to be highly tolerated outside stadiums in England. In fact I've purchased tickets from scalpers in direct view of police officers, and no problems.

That's all right then.

I don't see any harm in giving people the fact to make their own decisions.

Touting football tickets is illegal in the UK, but it's also true that 1000's of people do it every week and generally the police on crowd control stick to that job rather than policing touts.

It's also true that they don't always ignore it and sometimes the local force will run an anti-touting operation alongside the usual crowd control. No one can predict what will happen on any given day. The risk of buying forged ticket or having a valid ticket cancelled because it was resold are pretty much the same everywhere and, obviously as it's illegal you have very little legal comeback if you get caught out. Buyer beware!

Not relevant to this question but it may be useful if this question comes up under another search: Football tickets are the only thing that it's illegal to tout in the UK; it's perfectly legal (AFAIK, IANAL etc.) to tout other sports, theatre and concert tickets etc. It's almost always against the T&Cs to resell tickets but that's a civil matter.