As I'm sure you've heard in many blog articles/websites/books, you really do have to dress for concealed carry. Massad Ayoob has an excellent section on this in his book "The Gun Digest Book of Concealed Carry," and one of the articles of clothing he mentions is a belt. The reason for this should be fairly obvious. Aside from your holster, the single most important piece of gear for keeping your firearm properly secured on your person is your belt. I would personally consider it every bit as important as the holster. Think of them as a complimentary system. Spending a lot of money on one while neglecting the other can easily lead to a failure of the system to perform as required, IE., a $100+ holster hanging from a cheap Wally World belt is going to sag and shift, at the very least becoming annoying, and at the worst allowing your firearm to move out of position (or fail), causing your firearm not be where it needs to be when you need it. Don't even get me started on the guy I saw carrying a $1k pistol in a Wally World holster hanging from a cheap cotton belt that probably came with the shorts he was wearing.
For my needs, I utilize two different belts: the Line One Belt from First Spear, and a Bianchi Fancy Stitched Leather Belt. I purchased the Line One Belt after seeing it online, and utilized it to carry my Raven Concealment holster and mag pouch for a Glock 19/TLR-1 combo. The Bianchi normally supports my Colt Lightweight Commander in a Fobus (I'm still waiting on my G-Code).
A little about the belts:
The First Spear belt is urethane coated nylon, and is 1.5 inches wide. You get your choice of black or tan (and everyone knows everything is cooler in tan). A major advantage of this particular belt is that because of the urethane, it is virtually impervious to the elements and the age old issue of leather stretch. It also requires very little upkeep. It looks good, and from a normal contact distance, looks like a standard pants belt. The price is also slightly cheaper than most quality leather belts. The downside is that this belt is normal belt thickness (approx 1/8"). It hasn't been an issue for me so far, but with a higher ride holster or a heavier gun, it could be prone to cant.
As the name implies, the Bianchi is brown leather with a stitched pattern, and is 1.75 inches wide. This has become my go-to belt. When paired with my Lightweight Commander, I never have to worry about my firearm moving or sagging. I actually bought the belt on the recommendation of a prior-service SEAL who had done PSD work and told me that his unit had issued the belts to them, and had never had an issue supporting their Sigs. The Bianchi is a little thicker than the First Spear (approx 3/16"), and between the extra thickness and width, provides a very stable platform for mounting a holster. On the downside, it is leather, it will require minor upkeep, and it will eventually stretch and need to be replaced. I don't consider this a major disadvantage, as nothing lasts forever, and just like you will eventually probably have to replace your holster (if you use leather), you will eventually have to replace this belt. It is a bit pricier than the First Spear, but after wearing it for the last few months, I consider the extra money worth it. The only annoying item I have found is that not all my pants have belt loops that are friendly to this width belt. It's something I will have to watch for as I buy new pants.
Overall, I prefer the Bianchi for its stability, and let's be honest, in a world of constant tactical nylon bombardment, there is still something enduring about good old fashioned leather.