Leveling kit, wheels, tires, exhaust are all pretty common mods. I have a Magnaflow stainless 14" muffler on my truck, and I had the resonator on the stock exhaust deleted as well. It was a pretty cost effective mod and the truck sounds much better than it did stock. Wheels are probably the first thing you can change to really make a vehicle stand out and that all depends on personal preference and what what you're planning on using the truck for. It's a tradesmen so I'm guessing it'll be doing some work then? Perhaps the leveling kit to get the truck to sit level, and some nice 17" to 20" aftermarket rims with all terrain tires would make it look that much better. There are some serious wheel and tire gurus on this forum that I'm sure would be more than happy to help if you ask.
Swapping out the headlights for a nice painted set also makes these trucks look about a million times better. A gentleman named JJ a legend of the forums runs the Retro Shop on here under the vendors section. He can custom paint your headlight bezels and set you up with retrofitted projector housings as well as HID headlights. His work really is second to none, I've been wanting to get a set of his lights for some time but have been waiting until the mod money is there to do so. JJ also does tinted tails. If you are DIY oriented you can do this yourself as well. Here's some links to both the Retro Shop page in the vendor section, and to the Retro Shop website as well as a picture of my tinted tail lights and third brake light.
http://www.ramforum.com/f96/
http://shop.retroshop.us/
Also you could debadge the truck and get rid off all of the ugly chrome badges that say RAM, or RAM 1500, or 4x4, etc... Debadging is an easy thing that you can do yourself. You said you wanted the truck to look clean, this would be the first thing I would do. Less badges = less clutter, and a cleaner look. Here's a link to a DIY on debadging.
http://www.ramforum.com/f75/how_debadge_right_way-4221/
Plasti-Dip might become your friend as well if you want to make things look a little different. It's a rubberized coating that comes in spray cans, or by the gallon depending on what you're buying it for and who you're buying it from. It comes in different colors and is the cheapest, most forgiving way to drastically change the look of something on your vehicle without breaking the bank. Here's a link to a DIY write-up I did that explains it in more detail.
http://www.ramforum.com/f75/plasti-dipping_diy-14508/
Bed stripes are also a pretty common touch on RAM pickups. Not everyone likes them but I think they look great. I've always had Travis at Kling's Designs
http://klingsdesigns.com/ make my stripes. He does an excellent job and will work with you to make them however you want them. I have mine put on by the pros because I don't have the patience nor the skill to perfect putting them on the truck. Here's a and older pic of my truck showing the stripes.
Lighting is also yet another way to change the look of your truck. Brighter headlights particularly HIDs look better and give you better visibility (win/win). LED bulbs give you brighter light output as well and can be bought in most colors to fit your needs. I swapped out my dome lights in my interior with cool white LED blubs, and my tail lights are currently 45 LED tower bulbs with resistors. I buy all of my lighting products through a company called Super Bright LEDS. They have a bulb finder that you can plug your year, make, and model into that will tell you exactly what LEDs to buy to replace your stock halogen bulbs. Here's a link to them:
http://www.superbrightleds.com/
Hope that helps. Welcome to RAM Forum. Get some pictures up on here so we can see what you got! If you have any other questions I'm always willing to help or to try and find someone who can help you. For reference here's some pics of my truck in it's various phases with some plasti-dip work done, debadging, etc...
This is how my truck looked last summer. Had set a black ebay headlights which leaked, so I returned them. I also plasti-dipped my chrome grille black to see how I liked the look. At this point the RAM badges on the doors, and all badges except for the ram head on the tailgate were removed.
This picture is how mine sits today. My front emblem has the RAM head blacked out with plasti-dip, the back portion is painted blue, and I still have a set of Vinyl bed stripes that I had custom made with Mopar logos.
