So first off all, congratulations to FC Barcelona, who deserved to win the competition this past season.

Though, the qualification rounds for the 2015/16 campaign have already started and there are a lot of hopefulls trying everything to make it to the biggest competition in european club football.
The second round of qualification will start next week and feature teams like past winners Celtic FC, who will play Icelands champions Stjarnan F.C.
Also part of that round will be teams like Partizan Belgrade, Dinamo Zagreb, Maccabi Tel Aviv, NK Maribor, Bate Borisov or Ludogoretz Razgrad.
To get a better look at the current phase of qualification just take look at the wikipedia page, which is up to date on everything Champions League.
The final will be played at the San Siro Stadium in Milan, Italy.

As we're watching who'll move on to the next rounds of CL qualification there are already five teams qualified for the playoff round(League route). Three of them are already seeded and those are Manchester United, Valencia and Bayer Leverkusen, while Lazio and Sporting are in limbo but most likely unseeded for the final round of qualification.
Teams that already qualified are:
Pot 1
Barcelona
Chelsea
Bayern
Juventus
Benfica
Paris Saint-Germain
Zenit Saint Petersburg
PSV Eindhoven
Pot 2
Real Madrid
Atletico Madrid
FC Porto
Arsenal London
Manchester City
Pot 2 or 3
FC Sevilla
Olympique Lyon
Dinamo Kyiv
Pot 3
Olympiacos
Galatasaray
Pot 3 or 4
AS Roma
Borussia Mönchengladbach
VFL Wolfsburg
Pot 4
K.A.A. Gent
I hope this overview gives you a better idea about the upcoming season.
So let's enjoy and discuss everything Champions League.