The official date for the release of the Razorwing Jetfighter is June 18th. This comes from a set of handouts to Games Workshop stores, with suggestions on how to promote new products. The pics are nice, especially the pic below, because it shows us the army all together. This way you can judge the size of the Razorwing and other models together. I'm not sure if this is really a leak, since the information was released to GW stores, but since it fell into the communities hands I stuck with the title leak.
No signs yet of anything else. Nothing past June 18th is known. The Razowing Jetfighter will probably come up for pre-order earlier. The words in the blue boxes that did not make the pics when I copied them, they give release dates. So we have Scourges, Talos/ Cronos, and Venoms on June 4th, and the Razorwing on June 18th.
Here is a link to the forum thread where you can find the link. There are a couple more pics of wyches and the battleforce box set contents. Warseer forum link. You have to search through the posts to find the link to the posts. I won't post a direct link to the pics.
The images come via spellscape.