RedLynx have today announced that Trials HD will be receiving a second DLC: the Big Thrills pack. The DLC is set for release in Q4 this year. Here's what the DLC will include, directly from the press release:
Forty new levels
With forty new professional tracks lovingly crafted by RedLynx's level designers, the new expansion will bring a whole new world of obsessive challenge and bone-crushing gameplay to the game's large and loyal fan base.
User-Created content
Unique with this release, RedLynx will also include ten user-created tracks, fully credited and featured right alongside the professional levels created by RedLynx. Everyone whose track is included will in addition receive cash or prizes, as well as in-game credit.
"We're thrilled - no pun intended - to present this contest with our partners at Microsoft," said Tero Virtala, CEO of RedLynx. "We couldn't think of a better way to give back to our fans than to give them the opportunity to have their work featured right alongside ours in the next expansion of the legendary Trials HD game."
Cash prizes
Gamers can visit BigThrillsContest.com to view the rules, the prizes, and the process for submitting a track for inclusion in the Trials HD - Big Thrills expansion pack.
While the press release didn't mention Achievements specifically, I'd say that it's a very safe bet that the new DLC will include a handful of new ones. If you factor in the now-confirmed gamerscore limit for XBLA games, allowing developers to add up to 150G extra to their game via DLC; as well as that leaked screenshot from April showing the game as having 300G (see here: Leaked Screenshots Reveal Upcoming XBLA Games?), you wouldn't be a fool to assume it'll add more gamerscore.
No mention of a price or release date either, other than that aforementioned Q4 2010 window.
EDIT: Thanks to forum user RadiantViper (and Joystiq, I guess...), I can now say that it has been confirmed that the new DLC will have "three new achievements with 50 more gamer points available, bringing Trials HD and its two DLCs to a total of 300." Put my speculation hat on for nothing!
We've got the full list of Trials HD achievements - check the list for guides to unlocking them.