I'd switch the chest press and flyes for incline presses and flyes. And if you've been doing the chest press with dumbbells move to a barbell or vise versa.

Arnold presses are great for the shoulders, and lateral raises will give you a great burn - wonderful finishing exercise.

Try wide grip bent over barbell rows and good mornings for the back.

Skull crushers (aka french press) or close grip barbell presses are the exercise for hitting all the heads of the tricep and one armed tricep extensions are a killer to finish off!

21's for biceps followed by concentration curls should leave you wondering if you can lift your water bottle afterward.

Lunges for the quads are a must - they will hurt, so be warned! You can keep the extensions as your secondary exercise for a good burn.

Deadlifts should be your primary exercise, so just switch hamstring exercises around and you'll notice a big difference.

Same goes for the calves, try the one legged ones first then do the others, but try them with a barbell if you've been using dumbbells.

www.fitsite.com and www.exrx.net all have exercise demos so you can get the form down right. Expect some major DOMS after switching things around!

Enjoy those next 4 weeks!
Nat