Maybe the biggest unknown returning cast of them all.  There’s been suggestions of an increased 3-4 approach with this defense as well which really adds possibly even more questions as well, considering the lack of depth at a potential nose tackle.  My observational thoughts is a little more limited here so feel free to help me fill in the gaps.
Returning players, first the defensive ends, just 5… or maybe only 3 depending on the message board rumor mill:
Josh Harris, (Sr) 6-5 251.  Josh returns as possibly the most experienced defensive lineman overall.  He’s a big guy and the heaviest defensive end on the team.  His season started slowly as he worked his way back in from a hamstring injury that cost him most of fall camp.  Josh, I believe, is the best returning pass rusher on the team.  That’s not to say someone else will rise above him this year, but based on prior observation – he’s the guy right now.
Zach Wagenmann, (Soph), 6-3.5 230.  Wags is a guy I really started paying attention to in fall camp, he’s a quick rusher and very agile.  He’s shown some good ability to rush right past tackles to get to the QB but when double-teamed he’d usually just get swallowed up and stopped.  If this 3-4 defense starts to take shape Wags would be an excellent pass-rushing OLB in that scheme.  Also, I’m still of the mind that Wags will be the next #37 on this squad.  Zach did well in ST last year, in many cases that’s carried over to success on defense as these guys progress, I’m hoping that’s the case here.
Garrett Riggio, (Sr), 6-3 245.  Someone posted on here that Riggio left the team in the late fall for family matters, but it wasn’t clear if he returned or not.  Garrett’s in class this semester, but I’m not sure if he’s working out/practicing/anything.  I hope he is, he’s a strong guy and adds depth at DE.  I’ve not seen much from him as a guy that gets to the QB a lot, but he’s also missed a lot of camps with nagging injuries I believe.
Clay Peirson, (Jr), 6-3, 239.  Also a message board rumor that he’s moving to TE.  Peirson seemed to have some challenges adapting to DE but started to get comfortable with it last year.  I guess we’ll see where he ends up.
Trevor Rehm, (So), 6-3 244.  Rehm was a non-factor in last years season but will need to be a big part of this team in 2011 if the DE situation doesn’t improve.  As fall camp progressed he started making some plays more and more, however he was buried in depth and so I didn’t see him much going up against 1st string players… if at all.
And now the DTs:
Chris Bradford, (Jr), 6-2 260.  Bradford like a few others (Bienemann & Crittenden) I’ve seen line up all over, in fact I think he played D-end for a bunch of fall camp.  People I’ve talked to have raved about his athleticism and quickness, I do wonder where we’ll see him out there, I think he might be better suited at defensive end.
Alex Bienemann, (Jr) 6-2 275.  No one just “fills in” for a departed Waldhauser, but that will be Alex’s job.  Fortunately he’s the right guy for it.  He’s another dude that’s played all over the D-line and for his size/weight is one of the quicker guys.  Think back to the UNI playoff game when Alex beat the interior line, chased the UNI QB in the endzone and might’ve had a safety/sack but had to hurdle over Bobby Alt (which he did).  In a 3-4 system Alex makes a great prospect for a D-end, in a 4-3 I’m seeing him as one of our starting tackles.
Tonga Takai, (So) 6-2 320.  The last two years in both spring and fall camp I’ve seen similar outcomes from Tonga.  A stong start and a less than stellar finish, in fall camp that carried over this year where Tonga found lots of playing time but really didn’t stand out like other DTs did.  Tonga’s got to be the big gap-stuffing nose tackle this defense needs, be it the 3-4 or 4-3.  Hopefully with further conditioning, maturity, practice, etc he’s found that balance and will be ready to be the “anchor” of the D-line.
Derek Crittenden, (RS-frosh) 6-3 250.  Derek’s another guy that’s rotated a bit.  If I recall correctly he sat out this fall.  Some posters on here have suggested he’s really bulked up.  If fall camp Derek started out slow but got rolling as it went on.  He’s a guy that the staff will really be pushing this spring I’d bet.
Jesse Ginn, (RS-frosh) 6-5 285.  Ginn opened fall camp in a huge way, he was wrecking the 2s/3s Oline for his short stint of playing but then some sort of leg/knee injury sealed his fate for the  season.  Lots of people watching were getting real excited about what this true freshman could possibly contribute, well now we’ll finally get to see.  I’m not sure if we’ll see Ginn this spring though.  He’s a guy that with 10-15 more pounds could also step up to play that NT type of guy if a 3-4 is what the defense is running, he can also play DE in a 3-4 as well.
Christian Licarrdi, (RS-frosh) 6-3 280.  Licarrdi came into fall camp slated for O-line, but injuries sent him over to DT, where he then hurt his shoulder and sat after the 1st or 2nd scrimmage.  Another guy I don’t expect to see practicing, also I’m not sure where they’ll play him at DT or OL….
Taylor Tuliapupu, (Jr) 6-0 280? – Egriz post saying he’s up to 280 and will be moving to Dline… not sure where though.  That seems like a better fit for him, if he’s seriously got this much weight on but can still carry over some of his quicks from playing as a linebacker he could make a pretty good addition to the Dline.
New guys coming in, but won’t be here until fall:
Bo Harris, 6-3 260

Tyrone Holmes, 6-4 265

Ryan Johnson 6-2.5 235

Zach Peevey 6-3 230

Caleb Kidder 6-5 240
Not a big shock looking at the returning players and the amount of unknowns that this staff really went after defensive line in this recruiting class.  Like many I see Kidder as the one guy in this group that could make an immediate splash, the others I’ll have to see more out of when fall camp starts.
A wild-guess on depth… well here goes, assuming a 4-3 here and what the heck I’m going to plug in guys we won’t see till fall:
1st string:  Harris/Bienemann/Takai/Wags

2nd string: Bradford/Crittenden/Ginn/Rehm (or Riggio?)

3rd string: Kidder/Liccardi/Tuliapupu/Riggio (or Rehm)