Give someone at a cam company a call like Comp Cams or Lunati (or similar) and they will recommend some cam grinds and the parts to match. Typically choosing a cam to match your heads and intake is the best way to go. If they're staying stock the choice should be pretty easy.
you won't need to change your heads. Depending on the lift of the new cam you can probably re-use the valve springs, rockers and pushrods too. If it were me, I'd go to a roller cam and lifters, just because you won't have any of the break in headaches that are typical of flat tappet's. Summit has some good "Summit brand" stuff that are nice on a budget, better than stock parts and I've had good luck with them.
if the lift on the cam is close to stock and you just want to add some LSA for a rumble all you'll need is a cam and lifters and you're ready to rock. BUT if you're already in there it's a good chance to freshen up some other things. I would look at replacing:
-Cam
-Lifters
-Rockers (go full roller)
-Timing set
-Pushrods (a set of good hardened ones)
-Valve springs (recommended for the cam, might as well replace the retainers and locks too)
seems like alot, but for a few hundred bucks you can have a REALLY smooth efficient valvetrain which does wonders to wake up an old motor.
Here's some parts I've used in the past and had very good success with on budget stock-ish builds:
I used this Summit 1105 flat tappet cam in a 400sbc and it was great. This is very inexpensive at $100 but made good power and had a good lope without being un-driveable. I used it because the truck it was in was a DD and I built the motor on a budget when I was a student, but I wouldn't hesitate to use it again. A roller cam and lifters will run you about $500 bucks
http://www.summitracing.com/parts/SUM-K1105/
I also used these full roller rockers. Again very cheap, and you free up alot of energy, I'd use them again in a second. They had good quality set screws and served me very well.
http://www.summitracing.com/parts/SUM-G6905/
If you call summit they'll recommend a spring for you, I happend on a set of comp beehives that I used, but you could likely find something suitable cheaper. A good set of hardened pushrods is about $30 bucks. and a timing set is about the same.
http://www.summitracing.com/parts/SUM-G6400/
http://www.summitracing.com/parts/SUM-G6600/
My 400sbc with these parts, an Edelbrock performer intake and Holly 780 on top, otherwise stock, made 380rwhp 400lbft on a dyno in my old '91 S-10
pretty cheap, and you'll be worry free for alot of things. (I rebuilt that whole motor for about 700-800 bucks, using all the stuff in this picture haha so it's a good time for a rebuild if you don't have the motor in anything yet)