Some interesting analysis of team consistency over the past three seasons. Some of the usual suspects up there but a few surprise outfits! http://www.thestatszone.com/articles/consistent-inconsistent-football-teams-europe Particularly fond of the Everton stat! They've finished in the same position on the same amount of points two seasons in a row!
Sunderland's consistency has been pretty remarkable too.....hard to think they can keep surviving by the skin of their teeth.
Looking at the longer-term and incorporating other competitions, surely Arsenal is the most consistent. Always finishes 2nd-4th in the league and round of 16 in CL. For a cup competition where you can draw pretty much anyone and any time, its especially remarkable that a team would exit in the same round 6 years in-a-row.