I would highly recommend the benchmade rukus or mini rukus. These are heavy duty knives and I belive the 2006 or 2007 knife of the year. The size and weight won't even be noticed as the knives are evenly balanced out. The stats on the rukus says 4.25" long, but I believe it is right at 4". As long as you don't go stabbing someone nobody is actually going to bust out a ruler and check. Don't be fooled by the name 'mini' on the mini-rukus, it is a 3.45" blade that is just as durable as the big brother. These knives are marked in the $200~$265 range, and of course they both have the axis lock which can hold up to 1000 pounds of pressure. Here are the stats for these two:
Benchmade Rukus blue class 610:
Blade Length: 4.25"
Blade Thickness: 0.150"
Blade Material: S30V Stainless Steel
Blade Hardness: 58-60HRC
Blade Style: Utility Drop-Point; Ambidextrous Dual Thumb-Studs
Weight: 7.70oz.
Clip: Black, Reversible, Tip-Up
Lock Mechanism: AXIS
Overall Length: 10.12"
Closed Length: 5.95"
Benchmade Mini-Rukus blue class 615:
Blade Length: 3.40"
Blade Thickness: 0.121"
Blade Material: S30V Premium Steel
Blade Hardness: 58-60HRC
Blade Style: Utility Drop-Point; Ambidextrous Thumb-Stud
Weight: 5.90oz.
Clip: Black, Deep Pocket, Tip-Up
Lock Mechanism: AXIS
Overall Length: 8.50"
Closed Length: 5.10"
For a more affordable folder with about the same durability, try looking up a SOG Vulcan, it is still new on the market, but believe me it is one hell of a knife! It has put up with me a lot. It is fairly thick for a folder and has the arc lock which can also be tested to 1000 pounds at the lock. This knife can be found for about a hundred dollars ($100) Here is the link for this knife,
http://sogknives.com/store/VL-01.html , and here are the stats for it as well:
SOG Vulcan:
Blade 3.5" x .16"
Overall Length 8.375"
Weight 5.0 oz.
Edge Straight
Steel VG-10
Handle Zytel
Finish Satin
Includes Reversible Pocket clip
Hope this helps, J.