How about Eric Daze? or a more recent example would be Cheechoo. I know Cheech is still playing but, I find a comeback to previous form nearly impossible at this point and the kid isn't even 30 yet.
How about Doug Gilmour, Doug Wilson, Wendell Clark.
Daze is not a bad example. Of course, it's injury-related.
Wilson played longer than most of his contemporaries and was an all-star in 1990. I would not count him.
Clark was seen as "old" even when he wasn't. When the Leafs reaquired him he was still just 29. As a 30-year old he put up a very solid 30+ goal season for a bad team. As a 32-year old he had another excellent season for Tampa Bay.
Gilmour? Depends what you mean by "washed up" - a shadow of his 127-point form? Sure. Not a good player anymore? Hogwash. He didn't fade any worse or at a faster rate than other stars of his stature from his generation did.
Not quite in this category (?) but an all-time classic nevertheless...
Came out of nowhere at age 31 and broke the NHL RECORD FOR POINTS with 82 points in only 48 games. Best total prior was only 36 points. Managed only 45 the next season. Out of NHL by age 34. His fluke record year was in 1943-44 - a weakened NHL due to the war was a factor. It took Gordie Howe to break his record with 86 in 1950-51..but that was in a 70-game season. Cain is the only retired scoring leader not in the HHOF.
I guess Markus Naslund doesn't quite fit the bill, but I was always surprised at how quickly he seemed to fade in Vancouver post-lockout (I guess it's a result of his various injuries). It doesn't help that he started to dominate pretty late (his first over-PPG season was at the age of 27). The guy did still put up respectable points right up till the end though.
terry sawchuk could've been considered to be "washed up" after he quit the bruins back in '57...
even though he continued to play for the next 13 years and won a cup in '67, he would never replicate those numbers of high shutouts and low GA during the early 50s (1950-1955) with detroit red wings......