I'm going to ignore 1a/1b situations, which rules out Boldin and Wayne (who are otherwise not comparable with true #2s). Really, Boldin and Wayne rule the roost this year, and some would argue that they're actually 1a's and not 1b's (I think Boldin, when healthy, is going to be the 1a to Fitzgerald's 1b, for instance).
Anyway, focusing on TRUE #2s, I see good value in the following situations. These aren't ranked in any exact order, but this is more or less the order I have them in.
Cincinatti- T.J. Whosyourmama is one of the VERY FEW WR2s who are proven performers.
Denver- I don't know if Rod Smith will be #2, or Javon Walker will be #2, or they'll wind up as 1a and 1b, but there's a lot of value here. I expect both WRs to finish in the top 24.
Carolina- Meshawn is a proven performer and a good chance to finish in the top 30, but the real value here is in the chance that Steve Smith gets injured (hamstring problems can be nagging), in which case Meshawn is the #1 in the best offense for #1 WRs in the league.
Seattle- Engram and D-Jax were both top-5 in the NFL in receptions before they got hurt, so the history of throwing the ball is there. Receptions tend to be more consistant from year-to-year than TDs, and Alexander isn't likely to have another record-breaking season, so I see good things this year from Engram (or Burleson, if you think he's the guy).
Dallas- Terry Glenn had a great season last year, and Owens is already nursing a hamstring injury.
Tampa Bay- Michael Clayton was the best rookie of the past 20 years not named Moss or Boldin. He had a bad year last year, so people tend to forget that, but this kid can flat-out play, and he's proven it at an NFL level. Nagging injuries are a concern, but if he's healthy this year, I expect a very nice rebound.
Jacksonville- Their #2 WR (Wilford) is far and away their most proven and battle-tested. I expect this to turn into a 1a/1b at some point in time.
Detroit- Yes, Corey Bradford is a scrub. On the other hand, he's the clear #2 in a very favorable offense. There's no way his ADP should be as low as it is.
St. Louis- Sure, they have a new offense. Sure, they already cut him once this offseason. With that said... come on, he's still Isaac Bruce. You could do a lot worse.
I'm sure I'm still forgetting someone, but that's a start.