Someone commented elsewhere that Miyano Mamoru and Ono Daisuke are developing their art much faster than Fukuyama Jun (and even Ishida Akira). Whilst I won't deny the talents of the former (have a listen to Durarara episode 3, and compare with Death Note and Kuroshituji), I'm wouldn't be so quick to label the latter as static. We tend to forget that their voices are actually quite distinct, and almost limited to school-aged characters, whereas someone like OnoD has a mid-range voice with qualities that can be adapted to a greater range of roles.
Nevertheless, although FukuJun and Ishitan are probably two of the most regularly typecast seiyuu, they have both accummulated pretty remarkable bodies of work. The roles that impressed me the most for both of them are not mainstream, and were achieved fairly early in their careers. Ishida-san, in particular, turned in a great performance as someone who aged from a young innocent 14yo to a wistful young man who lost everything but eventually regained a short time of bittersweet happiness.
The second season of Code Geass turned a lot of people off FukuJun's extravagant Lelouch, which is unfortunate, as it really was a groundbreaking role for him. Ironically, most fans who know him because of Lelouch feel that he is typecast for that voice, when in fact, it is far more normal to hear him voice someone like Luca (Macross Frontier). Personally, I really like his character on a drama cd a couple of years before Geass, where he was able to create the subtler range of emotions of someone who fell into a one-sided love. There is also one anime role that I think only the most serious of fans will recognise FukuJun in. I only listened to about 15 seconds of the character speaking 'normally' before I decided that I really didn't want to go any further, just in case it just went into...one of those scenes... But the point is, I didn't recognise him at all, a far cry from the "Ah! that's FukuJun" moment I had for Durarara.
Because of the nature of the industry, it's actually not very easy for most anime fans to fully appreciate the whole body of a seiyuu's work, particularly for male artists, because BL is where most fujoshi part with their money. (I would say that there aren't as many questionable roles for female seiyuu, because there is a lot more demand for the 'cute, demure girlfriend' than for R-rated material.) Personally, I'll never be able to hear all the work that any seiyuu has recorded - nor do I want to, really, as some things are definitely just a waste of time, or a blow to the conscience, no matter how much I love someone's voice - but I wouldn't be so quick to dismiss someone who sounds the same in all the works I've heard them in.