Now that I've owned pretty much every sub-$400 lens at least once :-) I am forced to conclude that the gear needs revamping. Oh yes, this is something I have a lot of experience in - but hopefully the learning process has allowed a few lessons to sink in.
Many ways can make sense with a set of lenses, and often one calls one lens 'ideal' then builds an imperfect kit around it. My problem comes from trying to solve simultaneous equations with a few variables left unsolved. I want weather-resistant lenses that all take the same filter size, are small and light and with the best IQ available for under $400 .. well, that really won't do, it's just too much to ask. Let's whittle it down a bit.
My current prime setup has been all-manual (focus and aperture) with 28, 50 and 135mm covered. I have owned more, including a 24mm and the DA 35/2.4, but I don't really use primes enough to keep a bunch of them around. A major gap in the 80-100mm range has been troublesome, but that's macro territory and therefore beyond my budget - yet somehow a Tamron SP 90mm f/2.8 fell through the auction system and into my lap. This non-Di model is one generation back from brand new - so now my primes are joined by one of the best lenses ever made. Maybe that's hyperbole, but the dyxum site (Minolta) rates it 4.8/5 and Pentax owners go 9.2/10 - so maybe it's real. My tests show it to be most impressive and likely my best current lens & perhaps best ever.
Late addition - found a DA 35/2.4 at Amazon, so my prime kit is becoming more automatic & less manual. At just over $150 this lens is easily worth having, even at the expense of the faster 50mm Rikenon. This deal puts a few other primes on the block.
As to mid-tele zooms, I've tried copies of the Pentax 50-200 (two flavors) and the 55-300 (in DAL and DA form) as well as a 100-300mm Quantaray (that one was better than I expected, by a long way). While I love the 50-200's compact size and 52mm filter size, the 55-300 does a better job in too many ways. I found a DA 55-300mm f/4.0-5.8 in excellent condition recently at a great price; when free shipping became available it became mine. That's really all the telephoto I need so let's finally stop working to improve on excellence.
I've tried nearly every available wide-standard zoom under $350: DA 18-55 (regular and WR) and 16-45 (twice), Sigma's 17-70 and 18-50 (both f/2.8-4.5) plus their original 18-200mm f/3.5-6.3, and Pentax' DA 18-135WR as well. Each was a good news/bad news lens, whether by design or by my luck of the draw. Since WR is really important to me, I have three choices: 18-55, 18-135 and the beyond-budget 16-50. Given these facts, the 18-55 will do until I hear of something that works better for me.
* The K200d is my tool of choice, but finances may be freeing up a bit for a lunge at the K-5 during its temporary (?) price drop. That would require very good optics to do its best.. and now I have some that easily qualify. On the other hand the k-r is about to be replaced, and if Ricoh/Pentax design a midrange WR body with the 12M- or 16M-pixel Sony sensor that will be worthy of my attention.