U2 had a pretty bad era in the late 90s/early 00s (the Atomic Bomb album in particular) but have since recovered.
Rihanna was awful until Rated R.
[/pissing on the parade]
erm, for me Blur never got bad. Then there's the one/two-album wonders that never had a chance to get bad (Sex Pistols, Nirvana)...
I've always seen Coldplay as consistently great but apparently liking them is like liking child porn
