Primitive attempt for a cruise control mod in GTASA.
It has some issues and I don't think I'll be able to fix them, maybe anyone else?
Anyway here it is:
Install it as usual in CLEO and while driving a vehicle (preferable a car) press C to enable cruising at the current speed and X or SPACE to stop cruising and revert to normal.

Drawbacks are: The car acts like is driven by magic, that is will not decrease speed while colliding with stuff and of course will take damage. It behaves strange while flipped as in the car will drag on its back as soon as you exit it (while flipped). The speed is actually lower than the current speed - I have no idea how to calculate the correct value for it.

Edit:

Since v 0.1 was kinda lame (cars moved like zombies of sort), here is v 0.2. It features a background tool written in c# that scans a file created by the cleo script which contains the cruise control status, the desired speed and the current speed. The exe sends keys for acceleration or brake intermittently in order to maintain the desired speed (I presume you would still have arrow UP and DOWN as acc and brk). I like this more since it's real and the car reacts to the environment normally. There are some tuning options as teh timer interval, the pipe file, etc. Just try and see.

Use the key 'C' to set and unset the cruise mode. Insist a little, it may not work at the slightest touch.
Install is straightforward, just copy the content form
I included the full source code of both the cleo script and the c# app, so anyone with ideas, please go ahead and help yourselves, just let me know 'coz I really wanna see some improved variant.

Anyway, stay tuned as I am researching into v 0.3 which will use a dll for speed set. The only drawback that might pop up is the fact that it would not be possible to send the keys to the process, but I'll workaround it I guess (anyone knows more about dll's in gtasa through cleo, is welcome to comment or PM or whatever).

Edit2:
Updated the .NET application by adding some more tuning options. Enjoy!