Here is a schematic I designed that demonstrates you how you could create an IR transceiver for your RaspberryPi. You can use this schematic with the LIRC software package to create your own universal remote. It’s hosted on Upverter and contains a parts list for where to purchase the parts I used.
June 1st, 2013: Thanks to some feedback and experimentation I’ve updated the schematic. This latest version reflects the best combination of parts I’ve found so far.
June 3rd, 2013: Two more schematic bugfixes.
June 8th, 2013: Read about the finished protoboard build in my Open Source Universal Remote - Parts & Picturse blog post.
If you have any suggestions for improvements feel free to tinker on it and submit them.
Update: Thanks to Steve in the comments for pointing out a few errors I had in the schematic.