Some new stuff is coming out of the sourceruns community in the near-ish future and I'm so excited I just have to talk to whoever I can about it.
Spider-Waffle's amazing "Half Hour Half-Life" from years ago is finally going to have a proper successor in HL22, a speedrun estimated to finish around the 22 minute mark being worked on by Spider-Waffle and Quadrazid.
http://www.youtube.com/watch?v=peR7nkqhnvU
their progress on the project can be kept up with here
https://docs.google.com/spreadsheet/ccc?key=0AivfAnPipM1cdEVrY2NiRVpmdVJqREQ3ZHd1TDAyc1E#gid=0
And HL2 Done Quick is getting redone on the modern source engine to take advantage of the implementation of ABH (Accelerated Back-Hop), which has provided us many an enjoyable Portal run. It doesn't have a proper teaser yet but the project is currently being referred to within the speedrunning community as "HL2:DWaHMoV", (HL2: Done with a High Magnitude of Velocity). Here's a little something to whet your appetite if you're not yet aware of the potential offered by by ABH.
http://www.youtube.com/watch?v=1-8Q0fIhXwg
There's a while to wait yet for this one, but various channels are dropping tantalizing clips of progress, this channel being one of the most notable.
If you want to try these things yourself:
for HL1, google New Gauge Half-Life, learn how to bhop, and find yourself some scripts.
for HL2, learn ABH and have fun flying around at mach 2. Until you graze a pebble and get sent flying into the skybox. But if you can avoid that it's a blast.