UEFA's Best Club Scorers of All Time

1. Pippo Inzaghi (Parma, Juventus, Milan) – 68 Goals
2. Raul Gonzalez (Real Madrid) – 68 Goals 
3. Gerd Muller (Bayern Munich) – 62 Goals
4. Andriy Shevchenko (Dynamo Kiev, Milan, Chelsea) – 62 Goals
5. Ruud van Nistelrooy (PSV, Manchester United, Real Madrid) – 60 Goals
6. Thierry Henry (Monaco, Juventus, Arsenal, Barcelona) – 59 Goals 
7. Henrik Larsson (Feyenoord, Celtic, Barcelona, Manchester United, Helsingborgs) – 59 Goals
8. Eusebio (Benfica) – 54 Goals
9. Alessandro Del Piero (Juventus) – 51 Goals
10. Alfredo Di Stefano (Real Madrid) – 50 Goals

I found these stats on Goal.com.  They had also had a small write up on each player.  Although goals isn't the only factor that determines the quality of a player,  having upwards of 50 in European competition helps out.