The Game Mechanics are the class of d20 Modern support. Also some great work by RPGObjects, and I humbly submit by my own 12 to Midnight. In fact, if you dig horror games I challenge you to check us out. Email me at Jackson@12tomidnight, and I'll cut you a deal if you have never purchased from us before. (Blatant self-promotion done!) Rich Redman, JD Wiker and Stan! are the most responsible for the great Modern stuff out there and I greatly admire them.
Also, there are some folks putting out great game aids, such as weapons books and such that are invaluable. All are easily found on RPGNow. I hope to see more print books for Modern come out, but till then, the PDFs are the best support available.
I think the "lack of support" folks probably have one particular type of modern game they want and this colors their perspective. For instance, there are the fantasy beings in the modern world types, cyberpunkers, Modern Military gamers, spycrafters, horror genres, and others that are all d20 Modern. But there is something for everyone out there, and the lists of products are growing.
Allow me one other plug, but not for my company. If you haven't checked out Savage Worlds by Pinnacle, your really missing out. Fast play and cool settings for any genre of gaming.
Lates,
Jackson