I'd have thought it you want to tighten it up you want something either with a bass cut, or with a bass knob. So that (at least in my experience) rules out things like the klon, OCD, etc.
If you like your TS I'm not sure I'd run round trying millions of very slight variations on the TS thing. I'm not sure there's going to be a ton (if any) difference between yours, the ts808, the maxon od808 (which is actually a ts10, yet it's the more popular one because of the name, who says guitarists are full of it?
), maxon od9 etc. EDIT: and yeah I realise I'm a total hypocrite saying that considering how many TS-types I have.
If you want to try some slight upgrades/mods on the TS thing that might be worth a try- visual sound route 808, digitech bad monkey and hardwire tube od, etc. etc. Whether they actually work any better (I'm not sure they do) is another thing, though- just because they're advertised as "improved" doesn't necessarily mean they'll work any better if you just want the "TS tightening up a high gain tube amp" thing (which you already have). In my experience those "improved" ones normally have the advantage if you want to use them as a standalone overdrive into a clean channel (or at least if you want to use some overdrive from the pedal, even if the amp is a bit crunchy). The "improved" ones often (though not always, and some give you the option of either sound) "fix" the mid hump and bass cut, which is great when used as a standalone OD, but actually works against you when tightening a high gain amp (at least, in my experience).
Boss SD1 is pretty nice. Sort of TS-ish, but a bit brighter/edgier. Cheap enough too to give it a shot. Daphon does a cheapo clone, but most of the time it's not all that much cheaper than the Boss version (though it doesn't seem to have the bypass bleed). I think the badass modified OD Agent Orange suggested is a glorified/"improved" SD1 (though I haven't tried it).
If you want to try something much more transparent, a timmy (or in my case the discontinued cheapo danelectro clone) is probably my favourite for that. Though it's far from the only one- the digitech screamin blues will do it on the cheap (and has a bass knob unlike the boss BD2 which it's, er, "inspired by"). It's also worth pointing out that (at least in my experience), the more transparent/flatter response ODs don't have the mid-boost and compression of tubescreamer-style overdrives, which I also think helps with tightening up a high gain amp.
Just to clarify- I haven't tried every single pedal I listed there, and I also don't have a 6505, that's based on boosting my own high gain amps (engl savage se, laney gh50L, jet city 50 watt head), and at pretty low home volumes.
