Lets start off with the first complete set of rumors as they were told. I have read where lots of information is getting lost. Afterwards (by scrolling down), is the latest updated information.
Via Stickmonkey 3/2/2011
Lots of internal rumbling on a 2nd wave of tyranids. I don't have timelines, but expect it to hit before end of year, but after dark eldar releases complete that codex.
First, a new tyrant model is soon to debut. It has options for the swarm lord. It has some slight differences from the current metal, but is basically similar. I do think it stands between an inch or more higher, but not as tall as a trygon. I did not have an existing tyrant to compare. Wings are supposedly in the kit, but I did not see those.
Second, a harpy has been done, and will either be in this release or in the "summer of flyers"
Next for plastic kits the tervigon is finalized. IMO it does not exactly meet the image in the codex, but if you squint it's close. The model is nice and definitely fits the line.
This is where it gets fuzzy. The tyrranofex is not at all shaped or sized IMO like the tervigon model. I did not have them side by side to compare, but lot of Internet speculation these kits would be combined. I don't see it. Some pieces like legs might have dual use, but I didn't see sprue cuts to tell there. If they are one kit, it will surprise me.
No word on mycetic spores... Either way. I would place a bet they are also coming, but I don't know anything solid.
For metals,
There is a doom and parasite sculpted. They look as expected. Doom is fairly dynamic, parasite is a bit bigger than I thought and will likely use the larger skimmer base.
Also someone mentioned old one eye is getting a new sculpt, but I don't know how much faith I place in that one yet.
And a new yrgarll genestealer in metal...think flash gitz
Updated Information via Stickmonkey 3/3/2011
Tyrant. Plastic.
Parasite. Vyper/wave serpent skimmer base, not flyer base.
Harpy. Flyer base. Harpy is about the size of a Valkyrie. While it's footprint is similar in size to the valk, it is by no means as bulky.
One thing I did not look closely at is the harpy/tyrant parts comparison. It's possible, though not probable, those might be a shared kit.
