Maker's and Weller are probably the best known and widely available wheaters. Pappy, as Huffy said, is the most famous. The Pappy and Weller line both come out of the Buffalo Trace distillery now.
Other wheated bourbons include Larceny (from Heaven Hill), Rebel Yell (from Luxco), Wyoming Whiskey (out of Wyoming) and Garrison Brothers (out of Texas). Larceny is a throwback to Old Fitzgerald that was purchased by Heaven Hill...it's really good.
As Huffy said, rye whiskey and high-rye bourbon is spicier or harsher on most people's palette. I'm not a fan of rye whiskey, which is over 50 percent rye in the mash bill. High-rye bourbon is hit and miss with me.
Bourbon has to be at least 51 percent corn in the mash bill. The second ingredient is usually rye or wheat, and then typically a small percentage of malted barley. Wheated bourbons are those with wheat in the mash bill rather than rye. Rye often adds spicy, peppery notes...and sometimes earthy notes as well.
Harshness can also come from proof as well. Many people just getting into bourbon should try things in the 80 to 100 proof range. Old Forester 86 proof is a great one...72% corn, 18% rye and 10% malted barley. Notice the low percentage of rye. Of course Buffalo Trace is another, low rye and 90 proof. Then there's wheated stuff like Maker's and Weller.
Once you get used to the proof, you can start drinking 100 proof and move up to some of the 120 and 130+ proof stuff, usually called Cask Strength or Barrel Strength...meaning it is straight out of the barrel and not proofed down (or cut) with water. The only thing that can be added to bourbon out of the barrel is water...otherwise, it's no longer bourbon.
Barrel Strength whiskey has much more depth of flavor. It's much more complex and really coats your tongue. Weller Antique at 107 proof is much better than regular Weller Special Reserve. In my opinion, Maker's Mark Cask Strength at around 110 proof is an even better version of regular Maker's. So much more flavor.
But if you are mixing, then go with the lower proof, cheaper stuff for sure.
Some people love bourbon, some don't. My dad thinks bourbon is just okay...he's a scotch guy. I don't like scotch at all. I do like Irish Whiskey. I had Redbreast 12 last night...super good and very smooth.
I kind of rambled there, but hope some of that is helpful.